Communication Method, Communications Apparatus, And System

ABSTRACT

One example method includes receiving first indication information through a higher layer signaling, the first indication information indicating an available codebook subset, receiving downlink control information, determining a precoding matrix corresponding to a transmission precoding matrix indicator (TPMI) and a transmission rank obtained from the downlink control information, where the precoding matrix belongs to the available codebook subset indicated by the first indication information, precoding a signal based on the determined precoding matrix, and sending the precoded signal to a network device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/930,864, filed on May 13, 2020, which is a continuation ofInternational Patent Application No. PCT/CN2018/114857, filed on Nov. 9,2018, which claims priority to Chinese Patent Application No.201711131566.8, filed on Nov. 15, 2017. All of the afore-mentionedpatent applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

This application relates to the wireless communications field, and morespecifically, to a communication method, a communications apparatus, anda system.

BACKGROUND

In a massive multiple-input multiple-output (Massive MIMO) technology,interference between a plurality of users and interference between aplurality of signal streams of a same user may be reduced throughprecoding, which helps improve signal quality, implement spatialmultiplexing, and improve spectrum utilization.

Currently, a plurality of transmission forms such as coherenttransmission, partial coherent transmission, and non-coherenttransmission are proposed for uplink transmission, so as to adapt todifferent scenarios. However, in a current uplink codebook, theforegoing plurality of transmission forms are not fully considered. Forexample, in codebooks with ranks of 2 and 3, only partial non-coherenttransmission is supported. In a codebook with a rank of 4, onlynon-coherent transmission is supported. Even if a terminal device has acorresponding capability, flexibility of a transmission form of theterminal device is limited by the current codebook.

SUMMARY

This application provides a communication method, a communicationsapparatus, and a system, to improve transmission flexibility of aterminal device.

According to a first aspect, a communication method is provided,including:

sending, by a network device, a precoding matrix indicator PMI and arank indication RI, where the PMI and the RI are used to indicate aprecoding matrix in a codebook, and a rank of the precoding matrix isgreater than 1; where

the codebook includes at least two types of a first-type precodingmatrix, a second-type precoding matrix, and a third-type precodingmatrix, each column vector of any matrix in the first-type precodingmatrix includes only one non-zero element, non-zero elements in any twocolumn vectors are located in different rows, at least one column vectorof any matrix in the second-type precoding matrix includes at least onezero element and at least two non-zero elements, each element in anymatrix in the third-type precoding matrix is a non-zero element, and anytwo column vectors of any matrix in the third-type precoding matrix areorthogonal to each other.

Based on the foregoing codebook, when a terminal device has acorresponding capability, the terminal device may communicate with oneor more network devices in at least two transmission forms of coherenttransmission, partial coherent transmission, and non-coherenttransmission. Therefore, transmission flexibility of the terminal deviceis improved, and different transmission forms are used, so thatdifferent transmission requirements can be met, and resource utilizationis improved.

Optionally, the PMI and the RI are carried in downlink controlinformation (DCI).

With reference to the first aspect, in some implementations of the firstaspect, the method further includes:

sending, by the network device, first indication information, where thefirst indication information indicates a set of available precodingmatrices, or the first indication information indicates an availablecodebook subset, and the codebook subset includes at least one type ofthe first-type precoding matrix, the second-type precoding matrix, andthe third-type precoding matrix.

Optionally, the first indication information is carried in higher layersignaling. For example, the higher layer signaling may include a RadioResource Control (RRC) message or a Media Access Control (MAC)-controlelement (CE) message.

Optionally, the first indication information is a codebook subsetrestriction (CSR).

The available precoding matrix is indicated by using the higher layersignaling, which may limit a bit quantity of the PMI, thereby reducingbit overheads of the PMI.

Optionally, the first indication information is a bitmap, the bitmapincludes at least one indication bit, and when the first indicationinformation indicates a set of available precoding matrices, eachindication bit is corresponding to one precoding matrix, and eachindication bit indicates whether the corresponding precoding matrix isan available precoding matrix.

Optionally, the first indication information is a bitmap, the bitmapincludes at least one indication bit, and when the first indicationinformation indicates an available codebook subset, each indication bitis corresponding to one codebook subset, and each indication bitindicates whether a precoding matrix in the corresponding codebooksubset is an available precoding matrix.

It should be understood that, indicating the available precoding matrixby using the bitmap is only one possible implementation. For example,the network device may further indicate different types of precodingmatrices by using different values of the indication bit carried in thefirst indication information.

With reference to the first aspect, in some implementations of the firstaspect, the method further includes:

sending, by the network device, second indication information, where thesecond indication information is used to indicate a set of codebookscorresponding to a discrete Fourier transform spread orthogonalfrequency division multiplexing DFT-s-OFDM waveform; or

sending, by the network device, third indication information, where thethird indication information is used to indicate a set of codebookscorresponding to a cyclic prefix-orthogonal frequency divisionmultiplexing CP-OFDM waveform, where

the set of codebooks corresponding to the DFT-s-OFDM waveform includesat least one codebook corresponding to at least one rank, each codebookin the set of codebooks corresponding to the DFT-s-OFDM waveformincludes the first-type precoding matrix and the second-type precodingmatrix, the set of codebooks corresponding to the CP-OFDM waveformincludes at least one codebook corresponding to at least one rank, eachcodebook in the set of codebooks corresponding to the CP-OFDM waveformincludes at least two types of the first-type precoding matrix, thesecond-type precoding matrix, and the third-type precoding matrix, eachcolumn vector of any matrix in the first-type precoding matrix includesonly one non-zero element, non-zero elements in any two column vectorsare located in different rows, at least one column vector of any matrixin the second-type precoding matrix includes at least one zero elementand at least two non-zero elements, each element in any matrix in thethird-type precoding matrix is a non-zero element, and any two columnvectors of any matrix in the third-type precoding matrix are orthogonalto each other.

Optionally, the second indication information is carried in higher layersignaling.

Optionally, the third indication information is carried in higher layersignaling.

The higher layer signaling may include, for example, an RRC message or aMAC-CE message.

It should be noted that the second indication information and the thirdindication information may be carried in two different pieces of higherlayer signaling, and the network device may send, at a same moment, onlyone of the higher layer signaling used to carry the second indicationinformation and the higher layer signaling used to carry the thirdindication information.

It should be further noted that if the codebook corresponding to theCP-OFDM waveform includes only the first-type precoding matrix and thesecond-type precoding matrix, the set of codebooks corresponding to theDFT-s-OFDM waveform and the set of codebooks corresponding to theCP-OFDM waveform are the same.

According to a second aspect, a communication method is provided,including:

receiving, by a terminal device, a precoding matrix indicator PMI and arank indication RI, where the PMI and the RI are used to indicate aprecoding matrix in a codebook, and a rank of the precoding matrix isgreater than 1; and

precoding a signal based on the precoding matrix determined by using thePMI and the RI, and sending a precoded signal, where

the codebook includes at least two types of a first-type precodingmatrix, a second-type precoding matrix, and a third-type precodingmatrix, each column vector of any matrix in the first-type precodingmatrix includes only one non-zero element, non-zero elements in any twocolumn vectors are located in different rows, at least one column vectorof any matrix in the second-type precoding matrix includes at least onezero element and at least two non-zero elements, each element in anymatrix in the third-type precoding matrix is a non-zero element, and anytwo column vectors of any matrix in the third-type precoding matrix areorthogonal to each other.

Based on the foregoing codebook, when the terminal device has acorresponding capability, the terminal device may communicate with oneor more network devices in at least two transmission forms of coherenttransmission, partial coherent transmission, and non-coherenttransmission. Therefore, transmission flexibility of the terminal deviceis improved, and different transmission forms are used, so thatdifferent transmission requirements can be met, and resource utilizationis improved.

Optionally, the PMI and the RI are carried in downlink controlinformation DCI.

With reference to the second aspect, in some implementations of thesecond aspect, the method further includes:

receiving, by the terminal device, first indication information, wherethe first indication information indicates a set of available precodingmatrices, or the first indication information indicates an availablecodebook subset, and the codebook subset includes at least one type ofthe first-type precoding matrix, the second-type precoding matrix, andthe third-type precoding matrix.

Optionally, the first indication information is carried in higher layersignaling. The higher layer signaling may include, for example, an RRCmessage or a MAC-CE.

The available precoding matrix is indicated by using the higher layersignaling, which may limit a bit quantity of the PMI, thereby reducingbit overheads of the PMI.

Optionally, the first indication information is a bitmap, the bitmapincludes at least one indication bit, and when the first indicationinformation indicates a set of available precoding matrices, eachindication bit is corresponding to one precoding matrix, and eachindication bit indicates whether the corresponding precoding matrix isan available precoding matrix.

Optionally, the first indication information is a bitmap, the bitmapincludes at least one indication bit, and when the first indicationinformation indicates an available codebook subset, each indication bitis corresponding to one codebook subset, and each indication bitindicates whether a precoding matrix in the corresponding codebooksubset is an available precoding matrix.

It should be understood that, indicating the available precoding matrixby using the bitmap is only one possible implementation. For example,the network device may further indicate different types of precodingmatrices by using different values of the indication bit carried in thefirst indication information.

With reference to the second aspect, in some implementations of thesecond aspect, the method further includes:

receiving, by the terminal device, second indication information, wherethe second indication information is used to indicate a set of codebookscorresponding to a discrete Fourier transform spread orthogonalfrequency division multiplexing DFT-s-OFDM waveform; or

receiving, by the terminal device, third indication information, wherethe third indication information is used to indicate a set of codebookscorresponding to a cyclic prefix-orthogonal frequency divisionmultiplexing CP-OFDM waveform, where

the set of codebooks corresponding to the DFT-s-OFDM waveform includesat least one codebook corresponding to at least one rank, each codebookin the set of codebooks corresponding to the DFT-s-OFDM waveformincludes the first-type precoding matrix and the second-type precodingmatrix, the set of codebooks corresponding to the CP-OFDM waveformincludes at least one codebook corresponding to at least one rank, eachcodebook in the set of codebooks corresponding to the CP-OFDM waveformincludes at least two types of the first-type precoding matrix, thesecond-type precoding matrix, and the third-type precoding matrix, eachcolumn vector of any matrix in the first-type precoding matrix includesonly one non-zero element, non-zero elements in any two column vectorsare located in different rows, at least one column vector of any matrixin the second-type precoding matrix includes at least one zero elementand at least two non-zero elements, each element in any matrix in thethird-type precoding matrix is a non-zero element, and any two columnvectors of any matrix in the third-type precoding matrix are orthogonalto each other.

Optionally, the second indication information is carried in higher layersignaling.

Optionally, the third indication information is carried in higher layersignaling.

The higher layer signaling may include, for example, an RRC message or aMAC-CE message.

It should be noted that the second indication information and the thirdindication information may be carried in two different pieces of higherlayer signaling, and the network device may send, at a same moment, onlyany one of the higher layer signaling used to carry the secondindication information and the higher layer signaling used to carry thethird indication information.

It should be further noted that if the codebook corresponding to theCP-OFDM waveform includes only the first-type precoding matrix and thesecond-type precoding matrix, the set of codebooks corresponding to theDFT-s-OFDM waveform and the set of codebooks corresponding to theCP-OFDM waveform may be the same.

According to a third aspect, an apparatus is provided. The apparatusprovided in this application has a function of implementing behavior ofthe network device or the terminal device in the aspects of theforegoing methods, and includes corresponding means configured toimplement the steps or the functions described in the aspects of theforegoing methods. The steps or the functions may be implemented byusing software, hardware, or a combination of the software and thehardware.

In a possible design, the apparatus includes one or more processors anda communications unit. The one or more processors are configured tosupport the apparatus in performing a corresponding function of thenetwork device in the foregoing method, for example, generating a PMIand an RI. The communications unit is configured to support theapparatus in communicating with another device, to implement a receivingand/or sending function, for example, send the PMI and the RI.

Optionally, the apparatus may further include one or more memories,where the memory is configured to couple to the processor and store aprogram instruction and/or data necessary for the network device. Theone or more memories may be integrated with the processor, or may beseparately disposed with the processor. This is not limited in thisapplication.

The apparatus may be a base station, a gNB, a TRP, or the like. Thecommunications unit may be a transceiver or a transceiver circuit.Optionally, the transceiver may be an input/output circuit or aninterface.

The apparatus may alternatively be a communications chip. Thecommunications unit may be an input/output circuit or an interface ofthe communications chip.

In another possible design, the apparatus includes a transceiver, aprocessor, and a memory. The processor is configured to control thetransceiver to send and receive a signal. The memory is configured tostore a computer program. The processor is configured to run thecomputer program in the memory, so that the apparatus performs themethod completed by the network device in the first aspect or anypossible implementation of the first aspect.

In a possible design, the apparatus includes one or more processors anda communications unit. The one or more processors are configured tosupport the apparatus in performing a corresponding function of theterminal device in the foregoing method, for example, determining aprecoding matrix based on a PMI and an RI, and precoding a signal. Thecommunications unit is configured to support the apparatus incommunicating with another device, to implement a receiving and/orsending function, for example, receive the PMI and the RI, or send aprecoded signal.

Optionally, the apparatus may further include one or more memories,where the memory is configured to couple to the processor and store aprogram instruction and/or data necessary for the apparatus. The one ormore memories may be integrated with the processor, or may be separatelydisposed with the processor. This is not limited in this application.

The apparatus may be an intelligent terminal, a wearable device, or thelike. The communications unit may be a transceiver or a transceivercircuit. Optionally, the transceiver may be an input/output circuit oran interface.

The apparatus may alternatively be a communications chip. Thecommunications unit may be an input/output circuit or an interface ofthe communications chip.

In another possible design, the apparatus includes a transceiver, aprocessor, and a memory. The processor is configured to control thetransceiver to send and receive a signal. The memory is configured tostore a computer program. The processor is configured to run thecomputer program in the memory, so that the apparatus performs themethod completed by the terminal device in the second aspect or anypossible implementation of the second aspect.

According to a fourth aspect, a system is provided, where the systemincludes the foregoing terminal device and network device.

According to a fifth aspect, a computer readable storage medium isprovided and is configured to store a computer program. The computerprogram includes an instruction used to perform the method in the firstaspect or any possible implementation of the first aspect.

According to a sixth aspect, a computer readable storage medium isprovided and is configured to store a computer program. The computerprogram includes an instruction used to perform the method in the secondaspect or any possible implementation of the second aspect.

According to a seventh aspect, a computer program product is provided,the computer program product includes computer program code, and whenthe computer program code runs on a computer, the computer is enabled toperform the method in the first aspect or any possible implementation ofthe first aspect.

According to an eighth aspect, a computer program product is provided,the computer program product includes computer program code, and whenthe computer program code runs on a computer, the computer is enabled toperform the method in the second aspect or any possible implementationof the second aspect.

In any possible implementation of the foregoing aspects, optionally, thefirst-type precoding matrix meets at least one of the following:

${W_{1} = {\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with W₁.

The precoding matrix may support that power equalization between antennaports is implemented, and total transmit power may be evenly allocatedto each antenna port, so that a requirement on performance of a poweramplifier of the terminal device can be reduced.

Optionally, the first-type precoding matrix meets at least one of thefollowing:

${W_{2} = {\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with W₂.

The precoding matrix may support that power equalization between signalstreams is implemented, and therefore transmit power may be fully usedto ensure signal quality.

Optionally, the first-type precoding matrix meets at least one of thefollowing:

${W_{4} = {\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with W₄.

The precoding matrix may support that power equalization between antennaports, total transmit power may be evenly allocated to each antennaport, so that a requirement on a power amplifier of the terminal devicecan be reduced.

Optionally, the first-type precoding matrix meets at least one of thefollowing:

$W_{5} = {{\frac{1}{\sqrt{3}}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{bmatrix}}.}$

or

a matrix that has a row and/or column transform relationship with W₅.

The precoding matrix may support that power equalization between signalstreams is implemented, and therefore transmit power may be fully usedto ensure signal quality.

Optionally, the second-type precoding matrix meets at least one of thefollowing:

${W_{8} = {\frac{1}{\sqrt{6}}\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with WA.

Optionally, φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j}, and j is an imaginary unit.

Alternatively, optionally, φ₁∈{1, √{square root over (½)}, √{square rootover (¼)}, √{square root over (⅛)}, √{square root over ( 1/16)}}, andφ₂∈{1, √{square root over (½)}, √{square root over (¼)}, √{square rootover (⅛)}, √{square root over ( 1/16)}}.

It should be understood that values of φ₁ and φ₂ may be the same or maybe different. This is not limited in this application.

The precoding matrix may support that power equalization between signalstreams is implemented, and therefore transmit power may be fully usedto ensure signal quality.

Optionally, the second-type precoding matrix meets at least one of thefollowing:

${W_{9} = {\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}H_{1}}},$

or

a matrix that has a row and/or column transform relationship with W₉, or

${W_{8} = {H_{2}\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with W₁₀,where

H₁ and H₂ are coefficient matrices. Optionally, φ₁∈{1,−1,j,−j},φ₂∈{1,−1, j, −j}, and j is an imaginary unit. Alternatively, optionally,φ₁∈{1, √{square root over (½)}, √{square root over (¼)}, √{square rootover (⅛)}, √{square root over ( 1/16)}}, and φ₂∈{1, √{square root over(½)}, √{square root over (¼)}, √{square root over (⅛)}, √{square rootover ( 1/16)}}.

It should be understood that values of φ₁ and φ₂ may be the same or maybe different. This is not limited in this application.

Optionally,

$H_{1} = {{\begin{bmatrix}\frac{1}{\sqrt{8}} & 0 & 0 \\0 & \frac{1}{4} & 0 \\0 & 0 & \frac{1}{\sqrt{8}}\end{bmatrix}\mspace{14mu}{or}\mspace{14mu} H_{1}} = {\begin{bmatrix}\frac{1}{\sqrt{8}} \\\frac{1}{4} \\\frac{1}{\sqrt{8}}\end{bmatrix}.}}$

Optionally,

$H_{1} = {{\begin{bmatrix}\frac{1}{\sqrt{8}} & 0 & 0 & 0 \\0 & \frac{1}{4} & 0 & 0 \\0 & 0 & \frac{1}{\sqrt{8}} & 0 \\0 & 0 & 0 & \frac{1}{4}\end{bmatrix}\mspace{14mu}{or}\mspace{14mu} H_{1}} = {\begin{bmatrix}\frac{1}{\sqrt{8}} & \frac{1}{4} & \frac{1}{\sqrt{8}} & \frac{1}{4}\end{bmatrix}.}}$

In the design of the precoding matrix, power equalization betweenantenna ports in an antenna port group can be implemented, and totaltransmit power may be evenly allocated to each antenna port, so that arequirement on a power amplifier of the terminal device can be reduced.

Optionally, the second-type precoding matrix includes at least one ofthe following:

${W_{11} = {\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}}},$

or

a matric that has a row and/or column transform relationship with W₈.

Optionally, φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j}, and j is an imaginary unit.

Optionally, φ₁∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}, and φ₂∈{1,√{square root over (½)}, √{square root over (¼)}, √{square root over(⅛)}, √{square root over ( 1/16)}}.

It should be understood that values of φ₁ and φ₂ may be the same or maybe different. This is not limited in this application. Powerequalization between streams may be implemented in the precoding matrix.

Optionally, a structure of the third-type precoding matrix includes atleast one of the following:

${U_{3}^{1} = \begin{bmatrix}b_{k_{1}} \\{\alpha\; b_{k_{2}}}\end{bmatrix}},$

or

a matrix that has a row and/or column transform relationship with U₃ ¹,or

${U_{3}^{2} = \begin{bmatrix}b_{k_{1}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

or

a matrix that has a row and/or column transform relationship with U₃ ²,or

${U_{3}^{3} = \begin{bmatrix}b_{k_{1}} & b_{k_{1}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {{- \alpha}\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

or

a matrix that has a row and/or column transform relationship with U₃ ³,or

${U_{3}^{4} = \begin{bmatrix}b_{k_{1}} & b_{k_{1}} & b_{k_{1} + {x_{1}O}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {{- \alpha}\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}} & {{- \alpha}\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

or

a matrix that has a row and/or column transform relationship with U₃ ⁴,or a matrix including any two or three columns in U₃ ⁴, or a matrixincluding any two or three columns in the matrix that has a row and/orcolumn transform relationship with U₃ ⁴, where

α∈{1,−1,j,−j}, j is an imaginary unit, b_(k) ₁ , b_(k) ₂ , b_(x) ₁ _(−x)₁ _(O), and b_(k) ₂ _(+x) ₂ _(O) are discrete Fourier transform DFTvectors and meet

${b_{k_{1}} = \left\lbrack \begin{matrix}1 \\e^{j\;\frac{2\;\pi\; k_{1}}{{{N/2} \cdot O}\;}}\end{matrix} \right\rbrack},{b_{k_{2}} = \left\lbrack \begin{matrix}1 \\e^{j\;\frac{2\;\pi\; k_{2}}{{{N/2} \cdot O}\;}}\end{matrix} \right\rbrack},{b_{k_{1} + {x_{1}O}} = \left\lbrack \begin{matrix}1 \\e^{j\;\frac{2\;\pi\;{({k_{1} + {x_{1}O}})}}{{{N/2} \cdot O}\;}}\end{matrix} \right\rbrack},{and}$${b_{k_{2} + {x_{2}O}} = \left\lbrack \begin{matrix}1 \\e^{j\;\frac{2\;\pi\;{({k_{2} + {x_{2}O}})}}{{{N/2} \cdot O}\;}}\end{matrix} \right\rbrack},$

is an antenna port quantity, N=4, O=2, x₁∈{0,1}, and x₂∈{0,1}.

For the structure of the precoding matrix, it does not need to requirethat two DFT vectors that constitute one column vector point to a samebeam direction. In this way, a selection range of the precoding matrixmay be expanded, thereby increasing a minimal Grassmannian distance ofthe codebook, and facilitating system performance improvement.

It should be noted that the precoding matrix may be obtained throughtransformation by using the structure of the precoding matrix providedabove. The “transformation” may include but is not limited to row and/orcolumn transform, and/or normalization processing.

Optionally, the precoding matrix in the third-type codebook subsetincludes W_(M) and

$W_{M} = {\frac{1}{\sqrt{M \times N}}{U_{3}^{M}.}}$

M is a rank, M is an integer greater than or equal to 1, N is theantenna port quantity. N≥M, and N is an integer.

Optionally, the third-type precoding matrix includes W_(M), where W_(M)includes M column vectors in W₀, and W₀ and any precoding matrix u in acodebook with a rank of 1 meet the following mathematical transformrelationship:

W ₀ =I−2uu ^(H) /u ^(H) u,

where M is a rank, M is an integer greater than or equal to 1, I is anidentity matrix, and u^(H) is a conjugate transpose matrix of u.

Optionally, the third-type precoding matrix includes W_(M), where W_(M)includes M precoding matrices in a codebook with a rank of 1, M is arank, and M is an integer greater than or equal to 1.

Based on the designs of the various precoding matrices enumerated above,a selection range of the precoding matrix can be expanded, therebyincreasing a minimal Grassmannian distance of the codebook, andfacilitating system performance improvement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a communications system of acommunication method applicable to an embodiment of this application;

FIG. 2 is a schematic flowchart of a communication method according toan embodiment of this application;

FIG. 3 is a schematic diagram of an antenna port according to anembodiment of this application;

FIG. 4 is a schematic diagram of a terminal device according to anembodiment of this application;

FIG. 5 is a schematic structural diagram of a network device accordingto an embodiment of this application; and

FIG. 6 is a schematic structural diagram of a communications apparatusaccording to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following describes technical solutions of this application withreference to accompanying drawings.

The technical solutions of the embodiments of this application may beapplied to various communications systems, such as, a Global System forMobile Communications (GSM) system, a Code Division Multiple Access(CDMA) system, a Wideband Code Division Multiple Access (WCDMA) system,a general packet radio service (GPRS), a Long Term Evolution (LTE)system, an LTE frequency division duplex (FDD) system, an LTE timedivision duplex (TDD) system, Universal Mobile Telecommunications System(UMTS), a Worldwide Interoperability for Microwave Access (WiMAX)communications system, a future 5th generation (5G) system, a new radioaccess technology (NR), or the like.

For ease of understanding the embodiments of this application, first acommunications system shown in FIG. 1 is used as an example to describein detail a communications system applicable to the embodiments of thisapplication. FIG. 1 is a schematic diagram of a communications system ofa communication method applicable to an embodiment of this application.As shown in FIG. 1, the communications system 100 includes a networkdevice 102 and a terminal device 106. The network device 102 may beconfigured with a plurality of antennas, and the terminal device mayalso be configured with a plurality of antennas. Optionally, thecommunications system may further include a network device 104, and thenetwork device 104 may also be configured with a plurality of antennas.

It should be understood that the network device 102 or the networkdevice 104 may further include a plurality of components (for example, aprocessor, a modulator, a multiplexer, a demodulator, or ademultiplexer) related to signal sending and receiving.

The network device may be any device that has a wireless transceiverfunction or a chip that can be disposed in the device. The deviceincludes but is not limited to: an evolved NodeB (eNB), a radio networkcontroller (RNC), a NodeB (NB), a base station controller (BSC), a basetransceiver station (BTS), a home base station (for example, Homeevolved NodeB or Home NodeB, HNB), a baseband unit (BBU), an accesspoint (AP) in a Wireless Fidelity (Wi-Fi) system, a wireless relay node,a wireless backhaul node, a transmission point (TRP or TP), and thelike, or may be a gNB or a transmission point (TRP or TP) in a 5G systemsuch as an NR system, one or one group of antenna panels (including aplurality of antenna panels) of a base station in a 5G system, or may bea network node forming a gNB or a transmission point, such as a basebandunit (BBU) or a distributed unit (DU).

In some deployment, the gNB may include a centralized unit (CU) and aDU. The gNB may further include a radio frequency unit (radio unit, RU).The CU implements a part of functions of the gNB, and the DU implementsa part of the functions of the gNB. For example, the CU implementsfunctions of a radio resource control (RRC) layer and a Packet DataConvergence Protocol (PDCP) layer, and the DU implements functions of aRadio Link Control (RLC) layer, a Media Access Control (MAC) layer, anda physical (PHY) layer. Information at the RRC layer may finally becomeinformation at the PHY layer, or may be converted from information atthe PHY layer. Therefore, in this architecture, higher layer signalingsuch as RRC layer signaling or PHCP layer signaling may also beconsidered as being sent by the DU, or being sent by the DU and the RU.It may be understood that the network device may be a CU node, a DUnode, or a device including a CU node and a DU node. In addition, the CUmay be classified into a network device in an access network RAN, or theCU may be classified into a network device in a core network CN. This isnot limited herein.

The terminal device may also be referred to as user equipment (UE), anaccess terminal, a subscriber unit, a subscriber station, a mobilestation, a mobile console, a remote station, a remote terminal, a mobiledevice, a user terminal, a terminal, a wireless communications device, auser agent, or a user apparatus. The terminal device in the embodimentsof this application may be a mobile phone, a tablet computer (Pad), acomputer with a wireless transceiver function, a virtual reality (VR)terminal device, an augmented reality (AR) terminal device, a wirelessterminal in industrial control, a wireless terminal in self driving, awireless terminal in remote medical, a wireless terminal in a smartgrid, a wireless terminal in transportation safety, a wireless terminalin a smart city, a wireless terminal in a smart home, or the like. Anapplication scenario is not limited in the embodiments of thisapplication. In this application, the foregoing terminal device and achip that can be disposed in the foregoing terminal device arecollectively referred to as a terminal device.

In the communications system 100, both the network device 102 and thenetwork device 104 may communicate with a plurality of terminal devices(such as the terminal device 106 shown in the figure). The networkdevice 102 and the network device 104 may communicate with any quantityof terminal devices similar to the terminal device 106. However, itshould be understood that a terminal device that communicates with thenetwork device 102 and a terminal device that communicates with thenetwork device 104 may be the same or may be different. The terminaldevice 106 shown in FIG. 1 may communicate with the network device 102and the network device 104 at the same time. However, this shows onlyone possible scenario. In some scenarios, the terminal device maycommunicate with only the network device 102 or the network device 104.This is not limited in this application.

It should be understood that, FIG. 1 is only a simplified schematicdiagram used as an example for ease of understanding. The communicationssystem may further include another network device or may further includeanother terminal device, which is not drawn in FIG. 1.

For ease of understanding the embodiments of this application, thefollowing briefly describes a process of processing a signal (forexample, including a reference signal or data) on a physical channel inan LTE system. A code word from a higher layer may be processed on aphysical channel, and the code word may be a coded (for example,including channel coding) bit stream. The code word is scrambled togenerate a scrambled bit stream. The scrambled bit stream undergoesmodulation mapping to obtain a modulation symbol stream. The modulationsymbol stream is mapped to a plurality of layers through layer mapping.For ease of differentiation and description, in the embodiments of thisapplication, a symbol obtained after layer mapping may be referred to asa layer-mapped signal stream (or referred to as a symbol stream or aspatial stream). The layer-mapped signal stream undergoes precoding toobtain a plurality of precoded signal streams (or referred to asprecoded symbol streams). After the precoded signal stream undergoesresource element (RE) mapping, the precoded signal stream is mapped to aplurality of REs. These REs are then modulated through orthogonalfrequency division multiplexing (OFDM) to generate OFDM symbol streams.The OFDM symbol streams are then transmitted through an antenna port.

However, a person skilled in the art should understand that the varioussignal streams mentioned in this application are modulation symbolstreams. It should be further understood that terms defined for ease ofdifferentiation, such as the layer-mapped signal stream and the precodedsignal stream, should not constitute any limitation on this application.This application does not exclude a possibility that other names areused in an existing or future protocol to replace the foregoing names.Although signal streams appearing at a plurality of places in thefollowing are not described in detail, a person skilled in the art mayunderstand, according to an execution sequence of the foregoingprocesses, specific meanings of signal streams at each place.

Based on the foregoing processing process, the network device 102 maysend downlink signals to a plurality of terminal devices by using aplurality of antennas, and the terminal device may send uplink signalsto a same network device (for example, the network device 102 shown inthe figure) or different network devices (for example, the networkdevice 102 and the network device 104 shown in the figure) by using aplurality of antennas. In a MIMO technology, interference between aplurality of users and interference between a plurality of signalstreams of a same user may be reduced through precoding.

Precoding may mean that when a channel state is known, ato-be-transmitted signal is pre-processed on a transmit end, that is,the to-be-transmitted signal is processed by using a precoding matrixthat matches a channel resource, so that the to-be-transmitted signalthat has been precoded is adapted to a channel, and complexity ofeliminating inter-channel impact on a receive end is reduced. Therefore,the transmit signal is precoded, so that received signal quality (forexample, a signal to interference plus noise ratio (SINR)) is improved.Therefore, transmission between a transmit end device and a plurality ofreceive end devices may be implemented on a same time-frequency resourcethrough precoding, that is, multi-user multiple-input multiple-output(MU-MIMO) is implemented. It should be noted that related description ofprecoding is only used as an example, and is not used to limit theprotection scope of the embodiments of this application. In a specificimplementation process, precoding may be further performed in anothermanner (for example, when a channel matrix cannot be learned of,precoding is performed by using a preset precoding matrix or in aweighted processing manner). Details are not described in thisspecification.

In a possible implementation, to obtain a precoding matrix that can beadapted to a channel, the transmit end device may first perform channelmeasurement by sending a reference signal, so as to determine arelatively accurate precoding matrix to precode a to-be-sent signal.Specifically, the transmit end device may be a network device, and thereceive end device may be a terminal device. The reference signal may bea reference signal used for downlink channel measurement, for example, achannel state information reference signal (CSI-RS). The terminal devicemay perform CSI measurement based on a received CSI-RS, and feed backCSI of a downlink channel to the network device. Alternatively, thetransmit end device may be a terminal device, and the receive end devicemay be a network device. The reference signal may be a reference signalused for uplink channel measurement, for example, a sounding referencesignal (SRS). The network device may perform CSI measurement based on areceived SRS, and indicate CSI of an uplink channel to the terminaldevice. The CSI may include, for example, a precoding matrix indicator(PMI), a rank indication (RI), and a channel quality indicator (CQI).

It should be understood that the enumerated reference signal used fordownlink channel measurement and the enumerated reference signal usedfor uplink channel measurement are merely examples for description, andshould not constitute any limitation on this application. For example,the reference signal used for downlink channel measurement may furtherbe a downlink demodulation reference signal (DMRS), a tracking referencesignal (TRS), or a phase tracking reference signal (PTRS). The referencesignal used for uplink channel measurement may further be an uplink DMRSor the like. In addition, this application does not exclude apossibility of defining other reference signals that have a same orsimilar function in a future protocol, and this application does notexclude a possibility of defining another existing reference signal as areference signal for channel measurement in a future protocol.

It should be further understood that a manner of determining theprecoding matrix by the transmit end device is not limited to theforegoing manner of performing channel measurement based on thereference signal. The transmit end device may further estimate a channelbased on reciprocity of an uplink channel and a downlink channel, forexample, estimate CSI of a downlink channel based on channel stateinformation (CSI) of an uplink channel. In this case, CSI of the uplinkchannel may be determined based on a reference signal (for example, anSRS) sent by the terminal device. A manner of determining the precodingmatrix is not limited in this application.

To improve transmission flexibility of the terminal device to adapt todifferent scenarios, a plurality of transmission manners (or precodingmanners) are currently proposed. The following briefly describes severaltransmission forms in an uplink transmission process of the terminaldevice in the embodiments of this application.

1. Coherent transmission: One layer-mapped signal stream may be precodedby using all configured transmit antenna ports, so as to form onespatial beam for sending. Spatial beams corresponding to differentlayer-mapped signal streams are different. This may be understood asbeamforming, to reduce interference and improve signal quality.

2. Non-coherent transmission: One layer-mapped signal stream may beprecoded and sent by using one transmit antenna port. Differentlayer-mapped signal streams use different transmit antenna ports, andtime-frequency resources used when different transmit antenna ports areused to send the layer-mapped signal streams may be the same. This maybe understood as antenna port selection, thereby improving resourceutilization.

3. Partial coherent transmission: One layer-mapped signal stream may beprecoded by using a part of configured transmit antenna ports, so as toform one spatial beam for sending. Transmit antenna ports used by atleast two layer-mapped signal streams are different, or at least twolayer-mapped signal streams are corresponding to different spatialbeams. Because different signal streams are sent by using differentspatial beams, the terminal device may communicate with differentnetwork devices by using a same time-frequency resource.

It can be learned that, the above-enumerated three transmission formsare mainly different in a precoding stage, and one layer-mapped signalstream is precoded separately by using different quantities of antennas.Therefore, the foregoing three transmission forms may also be referredto as precoding manners.

The above-enumerated three transmission forms may be applied todifferent scenarios, and different terminal devices have differentcapabilities of supporting transmission forms. Some terminal devices maysupport the foregoing three transmission forms, and some terminaldevices may support only one or two of the foregoing three transmissionforms. If a codebook does not support a plurality of transmission forms,transmission flexibility of the terminal device may be significantlylimited.

In view of this, this application provides a communication method, so asto support the foregoing plurality of possible transmission forms andimprove transmission flexibility.

The following describes in detail the embodiments of this applicationwith reference to the accompanying drawings.

It should be understood that the technical solutions of this applicationmay be applied to a wireless communications system, for example, thecommunications system 100 shown in FIG. 1. The communications system mayinclude at least one network device and at least one terminal device,and the network device and the terminal device may communicate with eachother by using a radio air interface. For example, the network device inthe communications system may be corresponding to the network device 102or the network device 104 shown in FIG. 1, and the terminal device maybe corresponding to the terminal device 106 shown in FIG. 1.

It should be further understood that, in the embodiments shown in thefollowing, first, second, third, fourth, fifth, sixth, and seventh aremerely used for ease of distinguishing between different objects, andshould not constitute any limitation on this application, for example,distinguishing between different indication information and differentindication fields.

Without loss of generality, the following describes in detail theembodiments of this application by using an interaction process betweenone terminal device and a network device as an example. The terminaldevice may be any terminal device that is in a wireless communicationssystem and that has a wireless connection relationship with the networkdevice. It may be understood that the network device may communicatewith a plurality of terminal devices that have a wireless connectionrelationship with the network device in the wireless communicationssystem based on a same technical solution. This is not limited in thisapplication.

FIG. 2 is a schematic flowchart of a communication method 200 accordingto an embodiment of this application from a perspective of deviceinteraction. As shown in FIG. 2, the method 200 may include step 210 tostep 240.

In step 210, a network device sends a PMI and an RI.

Correspondingly, in step 210, a terminal device receives the PMI and theRI.

Specifically, the PMI and the RI may be used to indicate a precodingmatrix in a codebook. The RI may be used to indicate a rank, and the PMImay be used to indicate the precoding matrix in the codebookcorresponding to the RI. In this embodiment of this application, therank (for example, denoted as M) indicated by the RI may be an integergreater than 1. In other words, the codebook may be a higher-ordercodebook.

In this embodiment of this application, the PMI is a piece of possibleindication information used to indicate a precoding matrix, and the PMImay also be referred to as a transmission PMI (TPMI). The RI is a pieceof possible indication information used to indicate a rank. In somecases, the RI may also be referred to as a TRI (Transmission RI). Itshould be understood that the PMI, the RI, the TPMI, and the TRI areonly specific forms used for indication information, and should notconstitute any limitation on this application. This application does notexclude a possibility of defining other indication information in afuture protocol to implement a same or similar function.

In addition, it should be further noted that the network device may sendone or more PMIs to the terminal device, and a quantity of PMIs is notlimited in this application. In the following, the quantity of PMIs sentby the network device to the terminal device and indicated informationare described in detail with reference to a specific manner ofindicating the precoding matrix.

Optionally, before step 210, the method further includes step 220: Thenetwork device determines the PMI and the RI.

In a possible implementation, the network device may determine the PMIand the RI based on a received reference signal (for example, an SRS).The network device may first estimate a channel matrix H based on thereference signal, and determine a rank of the channel matrix, that is, aquantity of columns of a precoding matrix, so that a codebookcorresponding to the rank can be determined. The network device mayfurther determine the precoding matrix from the codebook correspondingto the rank. It may be understood that precoding matrices included inthe codebook corresponding to the rank may be understood as a set ofcandidate precoding matrices. The network device may determine, from theset of candidate precoding matrices, a precoding matrix (denoted as atarget precoding matrix for ease of differentiation and description)that is adapted to a current channel. For example, the target precodingmatrix is determined by using a degree of proximity between a candidateprecoding matrix and an ideal precoding matrix as metrics. The idealprecoding matrix may be a precoding matrix calculated based on thechannel matrix H.

For example, the network device may determine the target precodingmatrix in a singular value decomposition (SVD) manner. Specifically,after measuring and obtaining the channel matrix H based on thereference signal, the network device may perform SVD on the channelmatrix H to obtain:

H=U·S·V ^(H),

where U and V^(H) are unitary matrices, S is a diagonal matrix, non-zeroelements (namely, elements on a diagonal) of the diagonal matrix aresingular values of the channel matrix H, and these singular valuesusually may be arranged in descending order. A conjugate transpose V ofthe right unitary matrix V^(H) is the ideal precoding matrix. In otherwords, the ideal precoding matrix is a precoding matrix calculated basedon the channel matrix H.

The network device may determine the degree of proximity between thecandidate precoding matrix and the ideal precoding matrix, where thedegree of proximity may be represented as, for example, but not limitedto, a distance between the candidate precoding matrix and the idealprecoding matrix (for example, but not limited to a Euclidean distance).The network device may perform the foregoing process on each candidateprecoding matrix, to obtain a degree of proximity between each candidateprecoding matrix and the ideal precoding matrix. A candidate matrix witha highest degree of proximity may be selected as the target precodingmatrix, and the target precoding matrix is the precoding matrix that isindicated by the network device to the terminal device by using the PMIand the RI.

It should be understood that a method for determining the idealprecoding matrix by performing SVD in the foregoing example is only onepossible implementation, and should not constitute any limitation onthis embodiment of this application. For example, the network device mayfurther determine the ideal precoding matrix by using a receiveralgorithm such as minimum mean square error (MMSE), zero-forcing (ZF),and maximum ratio combining (MRC). It should be further understood thata method for determining the target precoding matrix based on theEuclidean distance in the foregoing example is only one possibleimplementation, and should not constitute any limitation on thisapplication. For example, the network device may further determine thetarget precoding matrix based on throughput maximization, SINRmaximization, or another criterion, so as to determine the PMI.

It should be further understood that a specific method for determiningthe channel matrix by the network device based on the reference signaland determining the rank and the precoding matrix based on the channelmatrix may be the same as that in the prior art. For brevity, detaileddescription of a specific process thereof is omitted herein. Inaddition, the network device may also determine the RI and the PMI basedon a channel state, and indicate the RI and the PMI to the terminaldevice, and does not determine the RI and the PMI based on the referencesignal. This is not limited in this application.

To support a more flexible transmission form, in this embodiment of thisapplication, the foregoing codebook may include at least two types of afirst-type precoding matrix, a second-type precoding matrix, and athird-type precoding matrix. In other words, the codebook may beclassified into the first-type precoding matrix and the second-typeprecoding matrix by type, or may be classified into the second-typeprecoding matrix and the third-type precoding matrix by type, or may beclassified into the first-type precoding matrix and the third-typeprecoding matrix by type, or may be classified into the first-typeprecoding matrix, the second-type precoding matrix, and the third-typeprecoding matrix by type. Each type of precoding matrix may becorresponding to one transmission form. In other words, the codebook maysupport at least two transmission forms.

Specifically, any matrix in the first-type precoding matrix may meetthat: each column vector includes only one non-zero element, andnon-zero elements in any two column vectors in each precoding matrix arelocated in different rows. The first-type precoding matrix may be usedby the terminal device to perform non-coherent transmission.

Any matrix in the second-type precoding matrix may meet that: at leastone column vector includes at least one zero element and at least twonon-zero elements. The second-type precoding matrix may be used by theterminal device to perform partial coherent transmission.

Any matrix in the third-type precoding matrix may meet that each elementis a non-zero element, and any two column vectors in a same matrix areorthogonal to each other. The third-type precoding matrix may be used bythe terminal device to perform coherent transmission.

The following describes in detail the three types of precoding matricesproposed in this application with reference to specific precodingmatrices.

It should be noted that, for ease of understanding only, severalpossible precoding matrices are shown for each type of precoding matrixin the following. However, this should not constitute any limitation onthis application. The precoding matrix proposed in this application maymeet at least one of the following enumerated precoding matrices. Inother words, any matrix that meets at least one of the followingenumerated precoding matrices should fall within the protection scopeclaimed by this application.

It should be further noted that, one or more possible precoding matricesare shown in the following for each type of precoding matrix. Some orall of the precoding matrices enumerated in the following for the threetypes of precoding matrices may be stored in the codebook, that is, thecodebook may store some or all of any two types of the followingenumerated three types of precoding matrices, or may store some or allof the three types of precoding matrices. This is not limited in thisapplication.

It should be noted that “meeting at least one of the following” is notlimited to “including at least one of the following”, and may furtherinclude “being obtained through transformation from at least one of thefollowing”. Herein, “transformation” may include but is not limited torow and/or column transform, and/or normalization processing.

For example, if it is assumed that the precoding matrix meets W₀, amatrix that has a row and/or column transform relationship with W₀, amatrix obtained after normalization processing is performed on W₀, and amatrix obtained after row and/or column transform is performed on thematrix obtained after normalization processing is performed on W₀ shouldfall within a protection scope of “meeting W₀” in this application. Thatis, the precoding matrix in the codebook may include at least one of thefollowing: W₀, or the matrix that has a row and/or column transformrelationship with W₀, or the matrix obtained by performing normalizationprocessing on W₀, or a matrix obtained by performing normalizationprocessing on the matrix that has a row and/or column transformrelationship with W₀.

In other words, W₀ may be understood as a possible structure (or a basicform) of the precoding matrix. A precoding matrix obtained by performingtransformation such as normalization processing on a basis of thisstructure also falls within the disclosed scope of the precoding matrixprovided in this embodiment of this application, and it may beunderstood that the precoding matrix meets an equation relationship ofW₀. In specific description, the “structure” may be omitted. However,because transformation performed on the precoding matrix, such asnormalization processing and/or row/column relationship transform has nosubstantial impact on application of the precoding matrix, a precodingmatrix obtained through transformation such as normalization processingand/or row/column relationship transform on the precoding matrix in thefollowing embodiments should also be understood as being within thedisclosed scope of the precoding matrix provided in this embodiment ofthis application.

During normalization processing, a coefficient may be allocated to eachelement in the basic form, so that a sum of power corresponding to theelements is less than or equal to 1. Optionally, normalizationprocessing includes but is not limited to multiplying the basic form bya constant coefficient, so as to adjust power of each layer, or power ofeach antenna port, or power of each stream. For example, normalizationprocessing is performed on W₀ to obtain

$\frac{1}{\sqrt{M \cdot N}}{W_{0}^{\prime}.}$

M is a rank, and N is an antenna port quantity. Then, a matrix that hasa row and/or column transform relationship with W₀ may include at leastone of: a matrix that has a row and/or column transform relationshipwith W₀, or

${\frac{1}{\sqrt{M \cdot N}}W_{0}^{\prime}},$

or a matrix that has a row and/or column transform relationship with

$\frac{1}{\sqrt{M \cdot N}}{W_{0}^{\prime}.\;\frac{1}{\sqrt{M \cdot N}}}$

may be referred to as a normalization coefficient and may be used toadjust the power of each stream. The normalization coefficient may be aconstant greater than 0.

It should be further noted that, in this embodiment of this application,if one precoding matrix includes a plurality of column vectors, it maybe understood that one precoding matrix may be a matrix obtained bysplicing the plurality of column vectors based on a pre-determinedquantity of rows and a pre-determined quantity of columns, or may be amatrix obtained by performing row and/or column transform, based on apredetermined quantity of rows and a predetermined quantity of columns,on the matrix obtained by splicing the plurality of column vectors.

The following describes in detail the three types of precoding matricesproposed in this application with reference to specific precodingmatrices.

1. First-type precoding matrix

(1) The rank is 2.

In a possible design, a structure of a precoding matrix with a rank of 2(namely, the basic form of the precoding matrix described above) maymeet:

${U_{1}^{21} = \left\lbrack \begin{matrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{matrix} \right\rbrack},$

or

a matrix that has a row and/or column transform relationship with U₁ ²¹.

The subscript in U₁ ²¹ represents the first-type precoding matrix, andthe superscript represents a first structure of the precoding matrixwith a rank of 2. Each column vector includes only one non-zero element,and non-zero elements in two column vectors are located in differentrows.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with U₁ ²¹ may include:

$\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack,{{{or}\mspace{14mu}\left\lbrack \begin{matrix}0 & 0 \\0 & 0 \\1 & 0 \\0 & 1\end{matrix} \right\rbrack}.}$

It should be understood that the above-enumerated matrices that have arow and/or column transform relationship with U₁ ²¹ are merely examplesfor description, and should not constitute any limitation on thisapplication. In the first-type precoding matrix, the structure of theprecoding matrix with a rank of 2 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with U₁ ²¹ different from the foregoing examples.

Optionally, the precoding matrix with a rank of 2 meets at least one ofthe following:

${W_{1} = {\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{matrix} \right\rbrack}},$

or

a matrix that has a row and/or column transform relationship with W₁.

½ is a normalization coefficient, or is referred to as a constantcoefficient. The precoding matrix is a matrix of four rows and twocolumns, that is, a four-antenna-port precoding matrix with a rank of 2.To meet power equalization between antenna ports, total transmit powermay be evenly allocated to each antenna port, so that a requirement on apower amplifier of the terminal device can be reduced. Normalizationprocessing means that ¼ of the total transmit power may be allocated toeach of the four antenna ports. That is, ¼ of the power may be allocatedto each row vector in the precoding matrix, and therefore anormalization coefficient

$\frac{1}{\sqrt{4}}.$

namely, ½ may be obtained. Therefore, W₁ and the matrix that has a rowand/or column transform relationship with W₁ may be considered asprecoding matrices that meet power equalization between antenna ports,and ½ may be considered as a normalization coefficient that meets powerequalization between antenna ports.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with W₁ may include:

${\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack},{{or}\mspace{14mu}{{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\0 & 0 \\1 & 0 \\0 & 1\end{matrix} \right\rbrack}.}}$

It should be understood that the above-enumerated W₁ and matrices thathave a row and/or column transform relationship with W₁ are merelyexamples for description, and should not constitute any limitation onthis application. In the first-type precoding matrix, the precodingmatrix with a rank of 2 may include at least one of the foregoingexamples, or may include a matrix that has a row and/or column transformrelationship with W₁ different from the foregoing examples.

For ease of differentiation and description, the above-enumerated W₁ andmatrices that have a row and/or column transform relationship with W₁may be referred to as type A precoding matrices. It should be understoodthat the type A precoding matrix may be understood as a sub-type of thefirst-type precoding matrix, and the type A precoding matrix may bedesigned based on power equalization allocation between antenna ports.

Optionally, the precoding matrix with a rank of 2 meets at least one ofthe following:

${W_{2} = {\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{matrix} \right\rbrack}},$

or

a matrix that has a row and/or column transform relationship with W₂.

$\frac{1}{\sqrt{2}}$

is a normalization coefficient. To meet power equalization betweenstreams, total transmit power may be evenly allocated to each stream.Therefore, transmit power may be fully used to ensure signal quality.Normalization processing means that ¼ of the total transmit power may beallocated to each antenna port. However, because each column vector inthe precoding matrix includes only one non-zero element, that is, eachlayer transmits a signal by using only one antenna port (namely, a rowincluding a non-zero element), power allocated to another antenna port(namely, a row including no non-zero element) may be used by an antennaport having a transmit signal (namely, a row including a non-zeroelement). That is, power of each antenna port may be improved, andtransmit power of each antenna port may be increased from ¼ to ½, andtherefore a normalization coefficient

$\frac{1}{\sqrt{2}}$

may be obtained. Therefore, W₂ and the matrix that has a row and/orcolumn transform relationship with W₂ may be considered as precodingmatrices that meet power equalization between streams (specifically,signal streams), and

$\frac{1}{\sqrt{2}}$

may be considered as a normalization coefficient that meets powerequalization between streams.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with W₂ may include:

${{\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack},{\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 1 \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 0 \\0 & 1\end{matrix} \right\rbrack},{or}}\mspace{11mu}$$\;{{\frac{1}{\sqrt{2}}\left\lbrack \begin{matrix}0 & 0 \\0 & 0 \\1 & 0 \\0 & 1\end{matrix} \right\rbrack}.}$

It should be understood that the above-enumerated W₂ and matrices thathave a row and/or column transform relationship with W₂ are merelyexamples for description, and should not constitute any limitation onthis application. In the first-type precoding matrix, the precodingmatrix with a rank of 2 may include at least one of the foregoingexamples, or may include a matrix that has a row and/or column transformrelationship with W₂ different from the foregoing examples.

For ease of differentiation and description, the above-enumerated W₂ andmatrices that have a row and/or column transform relationship with W₂may be referred to as type B precoding matrices. It should be understoodthat the type B precoding matrix may be understood as another sub-typeof the first-type precoding matrix, and the type B precoding matrix maybe designed based on power equalization allocation between signalstreams.

It should be understood that the above-enumerated W₁ and matrices thathave a row and/or column transform relationship with W₁, W₂ and matricesthat have a row and/or column transform relationship with W₂ are merelyexamples for description, and should not constitute any limitation onthis application. The precoding matrix with a rank of 2 may furtherinclude a matrix obtained by performing other normalization processingon U₁ ²¹, or a matrix that has a row and/or column transformrelationship with the matrix obtained by performing normalizationprocessing on U₁ ²¹.

In another possible design, the structure of the precoding matrix with arank of 2 may meet:

${U_{1}^{22} = \left\lbrack \begin{matrix}\beta_{1} & 0 \\0 & \beta_{2} \\0 & 0 \\0 & 0\end{matrix} \right\rbrack},$

a matrix that has a row and/or column transform relationship with U₁ ²².

The subscript in U₁ ²² represents the first-type precoding matrix, andthe superscript represents a second structure of the precoding matrixwith a rank of 2. Each column vector includes only one non-zero element,and non-zero elements in two column vectors are located in differentrows. In this design, power allocated to each antenna port or eachstream may be unbalanced.

Optionally, β₁ and β₂ meet β₁ ²+β₂ ²≤1

For example, a maximum value β_(max) may be given, β_(max)>0, β₁∈[0,β_(max)], and β₂∈[0, β_(max)].

It should be understood that values of β₁ and β₂ may be the same or maybe different. This is not limited in this application.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with U₁ ²² may include:

$\left\lbrack \begin{matrix}\beta_{1} & 0 \\0 & 0 \\0 & \beta_{2} \\0 & 0\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}\beta_{1} & 0 \\0 & 0 \\0 & 0 \\0 & \beta_{2}\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}0 & 0 \\\beta_{1} & 0 \\0 & \beta_{2} \\0 & 0\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}0 & 0 \\\beta_{1} & 0 \\0 & 0 \\0 & \beta_{2}\end{matrix} \right\rbrack,{{{or}\mspace{14mu}\left\lbrack \begin{matrix}0 & 0 \\0 & 0 \\\beta_{1} & 0 \\0 & \beta_{2}\end{matrix} \right\rbrack}.}$

Optionally, the precoding matrix with a rank of 2 may meet at least oneof the following:

${W_{3} = {\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & \gamma \\0 & 0 \\0 & 0\end{matrix} \right\rbrack}},{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & \gamma \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 \\0 & 0 \\0 & 0 \\0 & \gamma\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & \gamma \\0 & 0\end{matrix} \right\rbrack},{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\1 & 0 \\0 & 0 \\0 & \gamma\end{matrix} \right\rbrack},{{or}\mspace{14mu}{{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 \\0 & 0 \\1 & 0 \\0 & \gamma\end{matrix} \right\rbrack}.}}$

This is equivalent to β₁=½ and β₂=½γ in U₁ ²² shown above, where γ∈{1,√{square root over (½)}, √{square root over (¼)}, √{square root over(⅛)}, √{square root over ( 1/16)}}.

It should be understood that the above-enumerated precoding matrices aremerely examples for description, and should not constitute anylimitation on this application. In the first-type precoding matrix, theprecoding matrix with a rank of 2 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with any one of the foregoing examples and thatis different from the foregoing examples.

In addition, the precoding matrix with a rank of 2 may further include amatrix obtained by performing other normalization processing on U₁ ²²,or a matrix that has a row and/or column transform relationship with thematrix obtained by performing normalization processing on U₁ ²².

For ease of differentiation and description, the above-enumerated W₃ andmatrices that have a row and/or column transform relationship with W₃may be referred to as type C precoding matrices. It should be understoodthat the type C precoding matrix may be understood as still anothersub-type of the first-type precoding matrix.

(2) The rank is 3.

In a possible design, a structure of a precoding matrix with a rank of 3may meet:

${U_{1}^{31} = \left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{matrix} \right\rbrack},$

a matrix that has a row and/or column transform relationship with U₁ ³¹.

The subscript in U₁ ³¹ represents the first-type precoding matrix, andthe superscript represents a first structure of the precoding matrixwith a rank of 3. Each column vector includes only one non-zero element,and non-zero elements in two column vectors are located in differentrows.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with U₁ ³¹ may include:

$\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack,{{or}\mspace{14mu}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack},{{{or}\mspace{14mu}\left\lbrack \begin{matrix}0 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack}.}$

It should be understood that the above-enumerated matrices that have arow and/or column transform relationship with U₁ ³¹ are merely examplesfor description, and should not constitute any limitation on thisapplication. In the first-type precoding matrix, the structure of theprecoding matrix with a rank of 3 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with U₁ ³¹ different from the foregoing examples.

Optionally, the precoding matrix with a rank of 3 meets at least one ofthe following:

${W_{4} = {\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{matrix} \right\rbrack}},$

a matrix that has a row and/or column transform relationship with W₄.

½ is a normalization coefficient. The precoding matrix is a matrix offour rows and three columns, that is, a four-antenna-port precodingmatrix with a rank of 3. To meet power equalization between antennaports, total transmit power may be evenly allocated to each antennaport. Normalization processing means that ¼ of the total transmit powermay be allocated to each antenna port, and therefore a normalizationcoefficient ½ may be obtained. Therefore, W₄ and the matrix that has arow and/or column transform relationship with W₄ may be considered asprecoding matrices that meet power equalization between antenna ports,and ½ may be considered as a normalization coefficient that meets powerequalization between antenna ports.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with W₄ may include:

${\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack},{{or}\mspace{14mu}{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack}},{{or}\mspace{14mu}{{\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack}.}}$

It should be understood that the above-enumerated W₄ and matrices thathave a row and/or column transform relationship with W₄ are merelyexamples for description, and should not constitute any limitation onthis application. The first-type precoding matrix may include at leastone of the foregoing examples, or may include a matrix that has a rowand/or column transform relationship with W₄ different from theforegoing examples.

For ease of understanding and description, the above-enumerated W₄ andmatrices that have a row and/or column transform relationship with W₄may be referred to as type A precoding matrices. It should be understoodthat the type A precoding matrix may be understood as a sub-type of thefirst-type precoding matrix. The type A precoding matrix may be designedbased on power equalization allocation between antenna ports.

Optionally, the precoding matrix with a rank of 3 meets at least one ofthe following:

${W_{5} = {\frac{1}{\sqrt{3}}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{matrix} \right\rbrack}},$

or

a matrix that has a row and/or column transform relationship with W₅.

$\frac{1}{\sqrt{3}}$

is a normalization coefficient. To meet power equalization betweenstreams, total transmit power may be evenly allocated to each stream.During normalization processing, it is assumed that total transmit powerat each layer is 1, and ¼ of the power may be allocated to each antennaport. However, because each column vector in the precoding matrixincludes only one non-zero element, that is, each layer transmits asignal by using only one antenna port (namely, a row including anon-zero element), power allocated to another antenna port (namely, arow including no non-zero element) may be used by an antenna port havinga transmit signal (namely, a row including a non-zero element). That is,power of each antenna port may be improved, and transmit power of eachantenna port may be increased from ¼ to ⅓, and therefore a normalizationcoefficient

$\frac{1}{\sqrt{3}}$

may be obtained. Therefore, W₅ and the matrix that has a row and/orcolumn transform relationship with W₅ may be considered as precodingmatrices that meet power equalization between streams, and

$\frac{1}{\sqrt{3}}$

may be considered as a normalization coefficient that meets powerequalization between streams.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with W₅ may include:

${\frac{1}{\sqrt{3}}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack},{{or}\mspace{14mu}{\frac{1}{\sqrt{3}}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack}},{{or}\mspace{14mu}{{\frac{1}{\sqrt{3}}\left\lbrack \begin{matrix}0 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{matrix} \right\rbrack}.}}$

It should be understood that the above-enumerated W₅ and matrices thathave a row and/or column transform relationship with W₅ are merelyexamples for description, and should not constitute any limitation onthis application. The first-type precoding matrix may include at leastone of the foregoing examples, or may include a matrix that has a rowand/or column transform relationship with W₅ different from theforegoing examples.

For ease of differentiation and description, the above-enumerated W₅ andmatrices that have a row and/or column transform relationship with W₅may be referred to as type B precoding matrices. It should be understoodthat the type B precoding matrix may be understood as another sub-typeof the first-type precoding matrix. The type B precoding matrix may bedesigned based on power equalization allocation between signal streams.

It should be understood that the above-enumerated W₄ and matrices thathave a row and/or column transform relationship with W₄, W₅ and matricesthat have a row and/or column transform relationship with W₅ are merelyexamples for description, and should not constitute any limitation onthis application. In the first-type precoding matrix, the precodingmatrix with a rank of 3 may further include a matrix obtained byperforming other normalization processing on U₁ ³¹, or a matrix that hasa row and/or column transform relationship with the matrix obtained byperforming normalization processing on U₁ ³¹.

In another possible design, the structure of the precoding matrix with arank of 3 may meet:

${U_{1}^{32} = \left\lbrack \begin{matrix}\beta_{1} & 0 & 0 \\0 & \beta_{2} & 0 \\0 & 0 & \beta_{3} \\0 & 0 & 0\end{matrix} \right\rbrack},$

or

a matrix that has a row and/or column transform relationship with U₁ ³².

The subscript in U₁ ³² represents the first-type precoding matrix, andthe superscript represents a second structure of the precoding matrixwith a rank of 3. Each column vector includes only one non-zero element,and non-zero elements in two column vectors are located in differentrows. Optionally, β₁, β₂, and β₃, meet β₁ ²+β₂ ²+β₃ ²≤1, where β₁∈[0,1], β₂∈[0, 1], and β₃∈[0, 1]. In this embodiment of this application,values of β₁, β₂, and β₃ may be defined in a protocol, and may be thesame or different for different precoding matrices or differentstructures of precoding matrices. This is not limited in thisapplication. In this design, power allocated to each antenna port oreach stream may be unbalanced.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with U₁ ³² may include:

$\left\lbrack \begin{matrix}\beta_{1} & 0 & 0 \\0 & \beta_{2} & 0 \\0 & 0 & 0 \\0 & 0 & \beta_{3}\end{matrix} \right\rbrack,\left\lbrack \begin{matrix}\beta_{1} & 0 & 0 \\0 & 0 & 0 \\0 & \beta_{2} & 0 \\0 & 0 & \beta_{3}\end{matrix} \right\rbrack,{{{or}\mspace{14mu}\left\lbrack \begin{matrix}0 & 0 & 0 \\\beta_{1} & 0 & 0 \\0 & \beta_{2} & 0 \\0 & 0 & \beta_{3}\end{matrix} \right\rbrack}.}$

It should be understood that the above-enumerated matrices that have arow and/or column transform relationship with U₁ ³² are merely examplesfor description, and should not constitute any limitation on thisapplication. In the first-type precoding matrix, the structure of theprecoding matrix with a rank of 3 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with U₁ ³² different from the foregoing examples.

Optionally, the precoding matrix with a rank of 3 may meet at least oneof the following:

${{W_{6} = {\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & \gamma_{1} & 0 \\0 & 0 & \gamma_{2} \\0 & 0 & 0\end{matrix} \right\rbrack}},{{or}\mspace{14mu}{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & \gamma_{1} & 0 \\0 & 0 & 0 \\0 & 0 & \gamma_{2}\end{matrix} \right\rbrack}},{{or}\mspace{14mu}{\frac{1}{2}\left\lbrack \begin{matrix}1 & 0 & 0 \\0 & 0 & 0 \\0 & \gamma_{1} & 0 \\0 & 0 & \gamma_{2}\end{matrix} \right\rbrack}},{or}}\mspace{14mu}$${\frac{1}{2}\left\lbrack \begin{matrix}0 & 0 & 0 \\1 & 0 & 0 \\0 & \gamma_{1} & 0 \\0 & 0 & \gamma_{2}\end{matrix} \right\rbrack}.$

This is equivalent to β₁=½, β₂=½γ₁, and β₃=½γ₂ in U₁ ³² shown above,where γ₁∈{1, √{square root over (½)}, √{square root over (¼)}, √{squareroot over (⅛)}, √{square root over ( 1/16)}}, and γ₂∈{1, √{square rootover (½)}, √{square root over (¼)}, √{square root over (⅛)}, √{squareroot over ( 1/16)}}. In this embodiment of this application. γ₁ and γ₂may be defined in a protocol, and values of γ₁ and γ₂ may be the same ordifferent for different precoding matrices or different structures ofprecoding matrices. This is not limited in this application.

It should be understood that the above-enumerated precoding matrices aremerely examples for description, and should not constitute anylimitation on this application. In the first-type precoding matrix, theprecoding matrix with a rank of 3 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with any one of the foregoing examples and thatis different from the foregoing examples.

In addition, the precoding matrix with a rank of 3 may further include amatrix obtained by performing other normalization processing on U₁ ³²,or a matrix that has a row and/or column transform relationship with thematrix obtained by performing normalization processing on U₁ ³².

For ease of differentiation and description, the above-enumerated W₆ andmatrices that have a row and/or column transform relationship with W₆may be referred to as type C precoding matrices. It should be understoodthat the type C precoding matrix may be understood as still anothersub-type of the first-type precoding matrix.

(3) The rank is 4.

In a possible design, a structure of a precoding matrix with a rank of 4may meet:

${U_{1}^{4} = \left\lbrack \begin{matrix}\beta_{1} & 0 & 0 & 0 \\0 & \beta_{2} & 0 & 0 \\0 & 0 & \beta_{3} & 0 \\0 & 0 & 0 & \beta_{4}\end{matrix} \right\rbrack},$

or

a matrix that has a row and/or column transform relationship with U₁ ⁴.

The subscript in U represents the first-type precoding matrix, and thesuperscript represents a first structure of the precoding matrix with arank of 3. Each column vector includes only one non-zero element, andnon-zero elements in two column vectors are located in different rows.Optionally, β₁, β₂, β₃, and β₄ meet β₁ ²+β₂ ²+β₃ ²+β₄ ²≤1, where β₁∈[0,1], β₂∈[0, 1], β₃∈[0, 1], and β₄∈[0, 1]. In this embodiment of thisapplication, values of β₁, β₂, β₃, and β₄ may be defined in a protocol,and may be the same or different for different precoding matrices ordifferent structures of precoding matrices. This is not limited in thisapplication. In this design, power allocated to each antenna port oreach stream may be unbalanced.

Optionally, the precoding matrix with a rank of 4 may meet at least oneof the following:

${W_{7} = {\frac{1}{2}\begin{bmatrix}1 & 0 & 0 & 0 \\0 & \gamma_{1} & 0 & 0 \\0 & 0 & \gamma_{2} & 0 \\0 & 0 & 0 & \gamma_{3}\end{bmatrix}}},$

a matrix that has a row and/or column transform relationship with W₇.

This is equivalent to β₁=½, β₂=½γ₁, β₃=½γ₂, and β₄=½γ₃ in U₁ ³² shownabove, where γ₁∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}, γ₂∈{1, √{squareroot over (½)}, √{square root over (¼)}, √{square root over (⅛)},√{square root over ( 1/16)}}, and γ₃∈{1, √{square root over (½)},√{square root over (¼)}, √{square root over (⅛)}, √{square root over (1/16)}}. In this embodiment of this application. γ₁, γ₂, and γ₃ may bedefined in a protocol, and values of γ₁, γ₂, and γ₃ may be the same ordifferent for different precoding matrices or different structures ofprecoding matrices. This is not limited in this application.

It should be understood that the above-enumerated precoding matrices aremerely examples for description, and should not constitute anylimitation on this application. In the first-type precoding matrix, theprecoding matrix with a rank of 4 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with any one of the foregoing examples differentfrom the foregoing examples.

In addition, the precoding matrix with a rank of 4 may further include amatrix obtained by performing other normalization processing on U₁ ⁴, ora matrix that has a row and/or column transform relationship with thematrix obtained by performing normalization processing on U₁ ⁴.

It should be noted that, in a current protocol, for example, in an LTEprotocol, some precoding matrices in a codebook with a rank of 4 maysupport non-coherent transmission. Therefore, first-type precodingmatrices in the codebook with a rank of 4 may include some or all ofprecoding matrices in the codebook with a rank of 4 in the LTE protocol,or may include some or all of precoding matrices with a rank of 4proposed in this application, or may include some or all of acombination of the foregoing two. This is not limited in thisapplication.

In addition, in the current protocol, for example, in the LTE protocol,a codebook with a rank of 1 may support non-coherent transmission.Therefore, first-type precoding matrices in the codebook with a rank of1 may include some or all of precoding matrices in the codebook with arank of 1 in the LTE protocol. For brevity, examples are not enumeratedherein one by one.

Based on the foregoing design, the codebook may supportfour-antenna-port non-coherent transmission with any quantity of layerswithin a range of [1, 4], which greatly improves transmissionflexibility. In addition, different requirements such as powerequalization between antenna ports or power equalization between streamsmay be met. In addition, based on non-coherent transmission, on a sametime-frequency resource, a same terminal device may send differentsignal streams on different antenna ports, or send signals to differentnetwork devices on different antenna ports, thereby improving resourceutilization.

It should be noted that type A, type B. and type C enumerated above maybe understood as sub-types of the first-type precoding matrix, and typeA, type B. and type C may be separately designed based on differentpower allocation manners. In addition, for different ranks, one or morepossible precoding matrices of type A, type B, and type C are separatelyenumerated above. At least one of type A, type B, and type C may bestored in the codebook, and higher layer signaling is used to indicate atype of an available precoding matrix.

2. Second-type precoding matrix

(1) The rank is 3.

In a possible design, a structure U of a precoding matrix with a rank of3 may meet:

${U_{2}^{3} = \begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

$\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{3}} = \begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & {- \varphi_{2}} & 0\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with, or

$\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & {- \varphi_{2}} & 0\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{3}} = \begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & \varphi_{1} & 0 \\\varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

${\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & \varphi_{1} & 0 \\\varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{3}} = \begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- \varphi_{1}} & 0 \\\varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}},}\;$

or a matrix that has a row and/or column transform relationship with.

$\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- \varphi_{1}} & 0 \\\varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}.$

The subscript in U₂ ³ represents the second-type precoding matrix, andthe superscript represents a rank of 3. Each column vector includes onlyat least two non-zero elements and at least one zero element.

Optionally, φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j}, and j is an imaginary unit.

Optionally, φ₁∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}, and φ₂∈{1,√{square root over (½)}, √{square root over (¼)}, √{square root over(⅛)}, √{square root over ( 1/16)}}.

It should be noted that, in this application, two possible value rangesof φ₁ and φ₂ are provided in this application, and values of φ₁ and φ₂may be any one of the examples. However, it should be noted thatregardless of which value range of φ₁ and φ₂ is used, it does not meanthat the values of φ₁ and φ₂ need to traverse the entire value rangesprovided above. φ₁∈{1,−1,j,−j} is used as an example, φ₁∈{1,−1,j,−j} maybe understood as φ₁∈A, and A is {1,−1,j,−j} or a subset of {1,−1,j,−j}.That is, φ₁ may meet φ₁∈{1,−1}, or φ₁∈{j, −j}, or φ₁∈{1,j}, orφ₁∈{−1,−j}, or the like. For brevity, examples are not enumerated hereinone by one. Similarly, for a value of V₂, refer to the foregoing relateddescription. For brevity, a same or similar case is not described below.

In this embodiment of this application, the values of A and S, may bedefined in a protocol, and may be the same or different for differentprecoding matrices or different structures of precoding matrices. Thisis not limited in this application.

To support partial coherent transmission, it needs to be ensured that atleast two antenna ports may perform coherent transmission, and there areat least two groups of antenna ports that are non-coherent. In otherwords, it is ensured that each group includes at least two antennaports, antenna ports in each group may perform coherent transmission,and antenna ports in different groups are independent of each other.Therefore, antenna ports may be grouped into at least two groups, andeach group includes at least two antenna ports. For four antenna ports,the antenna ports may be grouped according to port numbers to obtain,for example, {1, 3} and {2, 4}, or {1, 2} and {3, 4}, or {1, 4} and {2,3}.

If a row number of each row in the precoding matrix is corresponding toa port number of an antenna port, U₂ ³ shows an example of groupingbased on the port numbers {1, 3} and {2, 4}. It may be understood thatantenna ports in a same group are corresponding to a same layer, thatis, antenna ports whose non-zero elements are located in a same columnvector are in one group. As shown in U, non-zero elements in the firstrow and the third row are located in both the first column and the thirdcolumn, and it may be considered that they belong to one group ofantenna ports (for example, denoted as an antenna port group #1); andnon-zero elements in the second row and the fourth row are located inthe second column, and it may be considered that they belong to anothergroup of antenna ports (for example, denoted as an antenna port group#2).

It is assumed that φ₁=φ₂, φ₁ and φ₂∈{1,−1,j,−j} are separatelysubstituted, and U₂ ³ and the matrix that has a row and/or columntransform relationship with U₂ may include:

${\varphi_{1} = {\varphi_{2} = 1}},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\1 & 0 & {- 1} \\0 & 1 & 0\end{bmatrix},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\1 & 0 & {- 1} \\0 & {- 1} & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & 1 & 0 \\1 & 0 & {- 1}\end{bmatrix},{\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- 1} & 0 \\1 & 0 & 1\end{bmatrix};}$ ${\varphi_{1} = {\varphi_{2} = {- 1}}},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\{- 1} & 0 & 1 \\0 & {- 1} & 0\end{bmatrix},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\{- 1} & 0 & 1 \\0 & 1 & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- 1} & 0 \\{- 1} & 0 & 1\end{bmatrix},{\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & 1 & 0 \\{- 1} & 0 & 1\end{bmatrix};}$ ${\varphi_{1} = {\varphi_{2} = j}},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\j & 0 & {- j} \\0 & j & 0\end{bmatrix},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\j & 0 & {- j} \\0 & {- j} & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & j & 0 \\j & 0 & {- j}\end{bmatrix},{\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- j} & 0 \\j & 0 & {- j}\end{bmatrix};}$ ${\varphi_{1} = {\varphi_{2} = {- j}}},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\{- j} & 0 & j \\0 & {- j} & 0\end{bmatrix},\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\{- j} & 0 & j \\0 & j & 0\end{bmatrix},\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- j} & 0 \\{j -} & 0 & j\end{bmatrix},{{{or}\mspace{14mu}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & j & 0 \\{- j} & 0 & j\end{bmatrix}}.}$

It should be understood that the above-enumerated matrices that have arow and/or column transform relationship with U are merely examples fordescription, and should not constitute any limitation on thisapplication. In the second-type precoding matrix, the structure of theprecoding matrix with a rank of 3 may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with U₂ ³ different from the foregoing examples.

Optionally, the structure U₂ ³ of the precoding matrix with a rank of 3meets at least one of the following:

${U_{2}^{3} = \begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & \varphi_{2} & 0 \\\varphi_{1} & 0 & {- \varphi_{1}}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

$\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & \varphi_{2} & 0 \\\varphi_{1} & 0 & {- \varphi_{1}}\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{3}} = \begin{bmatrix}1 & 1 & 0 \\0 & 0 & 1 \\\varphi_{1} & {- \varphi_{1}} & 0 \\0 & 0 & \varphi_{2}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

$\begin{bmatrix}1 & 1 & 0 \\0 & 0 & 1 \\\varphi_{1} & {- \varphi_{1}} & 0 \\0 & 0 & \varphi_{2}\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{3}} = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 1 \\\varphi_{2} & 0 & 0 \\0 & \varphi_{1} & {- \varphi_{1}}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship

$\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 1 \\\varphi_{2} & 0 & 0 \\0 & \varphi_{1} & {- \varphi_{1}}\end{bmatrix}.$

Optionally, φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j}, and j is an imaginary unit.

Optionally, φ₁∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}, and φ₂∈{1,√{square root over (½)}, √{square root over (¼)}, √{square root over(⅛)}, √{square root over ( 1/16)}}.

In this embodiment of this application, values of φ₁ and φ₂ may bedefined in a protocol, and may be the same or different for differentprecoding matrices or different structures of precoding matrices. Thisis not limited in this application.

Optionally, the structure U₂ ³ of the precoding matrix with a rank of 3includes at least one of the following:

${U_{2}^{3} = {\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\\theta_{1} & 0 & 0 \\0 & \theta_{2} & 0 \\0 & 0 & \theta_{3}\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\\theta_{1} & 0 & 0 \\0 & \theta_{2} & 0 \\0 & 0 & \theta_{3}\end{bmatrix}},{{or}\mspace{14mu}{\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & \theta_{2} & 0 \\\theta_{1} & 0 & 0 \\0 & 0 & \theta_{3}\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & \theta_{2} & 0 \\\theta_{1} & 0 & 0 \\0 & 0 & \theta_{3}\end{bmatrix}},{{or}\mspace{14mu}{\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & \theta_{2} & 0 \\0 & 0 & \theta_{3} \\\theta_{1} & 0 & 0\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & \theta_{2} & 0 \\0 & 0 & \theta_{3} \\\theta_{1} & 0 & 0\end{bmatrix}},{{or}\mspace{14mu}{\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\1 & 0 & 0 \\\theta_{1} & 0 & 0 \\0 & 0 & \theta_{3}\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\1 & 0 & 0 \\\theta_{1} & 0 & 0 \\0 & 0 & \theta_{3}\end{bmatrix}},{{or}\mspace{14mu}{\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\1 & 0 & 0 \\0 & 0 & \theta_{3} \\\theta_{1} & 0 & 0\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\1 & 0 & 0 \\0 & 0 & \theta_{3} \\\theta_{1} & 0 & 0\end{bmatrix}},{{or}\mspace{14mu}{\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\0 & 0 & \theta_{3} \\1 & 0 & 0 \\\theta_{1} & 0 & 0\end{bmatrix}}},$

or a matrix that has a row and/or column transform relationship with

${\frac{1}{2}\begin{bmatrix}0 & \theta_{2} & 0 \\0 & 0 & \theta_{3} \\1 & 0 & 0 \\\theta_{1} & 0 & 0\end{bmatrix}}.$

θ₁∈{1, √{square root over (½)}, √{square root over (¼)}, √{square rootover (⅛)}, √{square root over ( 1/16)}}θ₂∈{1, √{square root over (½)},√{square root over (¼)}, √{square root over (⅛)}, √{square root over (1/16)}}, and θ₃ ∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}. In thisembodiment of this application, values of θ₁, and θ₂ may be defined in aprotocol, and may be the same or different for different precodingmatrices or different structures of precoding matrices. This is notlimited in this application.

Optionally, the precoding matrix with a rank of 3 meets at least one ofthe following:

${W_{8} = {\frac{1}{\sqrt{6}}\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}}},$

a matrix that has a row and/or column transform relationship with W₅.

It may be further learned from U₂ ³ that, the antenna port group #1 maybe used to send signals of two layers, that is, two streams, and theantenna port group #2 may be used to send a signal of one layer, thatis, one stream. To ensure power equalization between different streams,a normalization coefficient may be obtained through normalizationprocessing. It is assumed that total transmit power is 1, and ⅓ of thepower may be allocated to each of the three layers. That is, ⅓ of thepower may be allocated to each row vector in the precoding matrix.Because coherent transmission may be performed on a signal stream ofeach layer through two antenna ports, ⅙ of the power may be furtherallocated to each of two antenna ports corresponding to each layer, anda normalization coefficient

$\frac{1}{\sqrt{6}}$

may be obtained. Therefore, W₈ and the matrix that has a row and/orcolumn transform relationship with W₈ may be considered as precodingmatrices that meet power equalization between streams, and

$\frac{1}{\sqrt{6}}$

may be considered as a normalization coefficient that meets powerequalization between streams.

By way of example and not limitation, the matrix that has a row and/orcolumn transform relationship with W₈ may include:

${{\frac{1}{\sqrt{6}}\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}},{\frac{1}{\sqrt{6}}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & \varphi_{1} & 0 \\\varphi_{2} & 0 & {- \varphi_{1}}\end{bmatrix}},{or}}\;$$\mspace{11mu}{{\frac{1}{\sqrt{6}}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 1 \\0 & {- \varphi_{1}} & 0 \\\varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}}.}$

It should be understood that the above-enumerated W₈ and matrices thathave a row and/or column transform relationship with W₈ are merelyexamples for description, and should not constitute any limitation onthis application. The second-type precoding matrix may include at leastone of the foregoing examples, or may include a matrix that has a rowand/or column transform relationship with W₈ different from theforegoing examples.

Optionally, the precoding matrix with a rank of 3 meets at least one ofthe following:

${W_{9} = {\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}\; H_{1}}},$

a matrix that has a row and/or column transform relationship with W₉.

H₁ is a coefficient matrix, or H₁ is a normalization coefficient matrix,that is, a matrix including normalization coefficients, and may be usedto adjust power of each antenna port or stream.

${H_{1} = {{\begin{bmatrix}\frac{1}{\sqrt{8}} & 0 & 0 \\0 & \frac{1}{4} & 0 \\0 & 0 & \frac{1}{\sqrt{8}}\end{bmatrix}\mspace{14mu}{or}\mspace{14mu} H_{1}} = {\begin{bmatrix}\frac{1}{\sqrt{8}} \\\frac{1}{4} \\\frac{1}{\sqrt{8}}\end{bmatrix}.}}}\;$

To equalize power of each antenna port in a same antenna port group,power allocated to each antenna port may be adjusted by using thenormalization coefficient matrix. For example, after a square of eachcoefficient in H₁ is substituted into the foregoing formula, an obtainedsum of power of all antenna ports is less than 1, and power allocated toantenna ports in each antenna port group is the same.

Optionally, the precoding matrix with a rank of 3 meets at least one ofthe following:

${W_{10} = {H_{2}\begin{bmatrix}1 & 0 & 1 \\0 & 1 & 0 \\\varphi_{1} & 0 & {- \varphi_{1}} \\0 & \varphi_{2} & 0\end{bmatrix}}}\;,$

a matrix that has a row and/or column transform relationship with W₁₀.

H₂ is a coefficient matrix, or H₂ is a normalization coefficient matrix,that is, a matrix including normalization coefficients, and may be usedto adjust power of each antenna port or stream.

$H_{2} = {{\begin{bmatrix}\frac{1}{\sqrt{8}} & 0 & 0 & 0 \\0 & \frac{1}{4} & 0 & 0 \\0 & 0 & \frac{1}{\sqrt{8}} & 0 \\0 & 0 & 0 & \frac{1}{4}\end{bmatrix}\mspace{14mu}{or}\mspace{14mu} H_{2}} = {\begin{bmatrix}\frac{1}{\sqrt{8}} & \frac{1}{4} & \frac{1}{\sqrt{8}} & \frac{1}{4}\end{bmatrix}.}}$

To equalize power of each antenna port in a same antenna port group,power allocated to each antenna port may be adjusted by using thenormalization coefficient matrix. For example, after a square of eachcoefficient in H₂ is substituted into the foregoing formula, an obtainedsum of power of all antenna ports is less than 1, and power allocated toantenna ports in each antenna port group is the same.

It should be understood that the above-enumerated precoding matriceswith a rank of 3 are merely examples for description, and should notconstitute any limitation on this application. In the second-typeprecoding matrix, the precoding matrix with a rank of 3 may include amatrix obtained after the structure U₂ ³ of the precoding matrix with arank of 3 is transformed (such as normalization processing and/or rowand/or column transform), or a matrix that is different from theforegoing examples and obtained after a matrix that has a row and/orcolumn transform relationship with any one of the structure U₂ ³ of theprecoding matrix with a rank of 3 is transformed.

(2) The rank is 4.

In a possible design, a structure U of a precoding matrix with a rank of4 may meet:

${U_{2}^{4} = \begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

$\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix},{{{or}\mspace{14mu} U_{2}^{4}} = \begin{bmatrix}1 & 1 & 0 & 0 \\0 & 0 & 1 & 1 \\\varphi_{1} & {- \varphi_{1}} & 0 & 0 \\0 & 0 & \varphi_{2} & {- \varphi_{2}}\end{bmatrix}},$

or a matrix that has a row and/or column transform relationship with

$\begin{bmatrix}1 & 1 & 0 & 0 \\0 & 0 & 1 & 1 \\\varphi_{1} & {- \varphi_{1}} & 0 & 0 \\0 & 0 & \varphi_{2} & {- \varphi_{2}}\end{bmatrix}.$

The subscript in U₂ ⁴ represents the second-type precoding matrix, andthe superscript represents a rank of 4. Each column vector includes onlyat least two non-zero elements and at least one zero element.

Optionally, Aφ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j}, and is an imaginary unit.

Optionally, φ₁∈{1, √{square root over (½)}, √{square root over (¼)},√{square root over (⅛)}, √{square root over ( 1/16)}}, and φ₂∈{1,√{square root over (½)}, √{square root over (¼)}, √{square root over(⅛)}, √{square root over ( 1/16)}}.

In this embodiment of this application, values of φ₁ and φ₂ may bedefined in a protocol, and may be the same or different for differentprecoding matrices or different structures of precoding matrices. Thisis not limited in this application.

If a row number of each row in the precoding matrix is corresponding toa port number of an antenna port, U₂ ⁴ shows an example of groupingbased on port numbers {1, 3} and {2, 4}. It may be understood thatantenna ports in a same group are corresponding to a same layer, thatis, antenna ports whose non-zero elements are located in a same columnvector are in one group. As shown in U₂ ⁴, non-zero elements in thefirst row and the third row are located in both the first column and thethird column, and it may be considered that they belong to one group ofantenna ports (for example, denoted as an antenna port group #3), andnon-zero elements in the second row and the fourth row are located inthe second column, and it may be considered that they belong to anothergroup of antenna ports (for example, denoted as an antenna port group#4).

It is assumed that φ₁=φ₂, values {1,−1, j,−j} of φ₁ and φ₂ areseparately substituted to obtain U₂ ⁴ that may include:

$\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\1 & 0 & {- 1} & 0 \\0 & 1 & 0 & {- 1}\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\{- 1} & 0 & 1 & 0 \\0 & {- 1} & 0 & 1\end{bmatrix},\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\j & 0 & {- j} & 0 \\0 & j & 0 & {- j}\end{bmatrix},{{{or}\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\{- j} & 0 & j & 0 \\0 & {- j} & 0 & j\end{bmatrix}}.}$

It should be understood that the above-enumerated structures of theprecoding matrices with a rank of 4 are merely examples for description,and should not constitute any limitation on this application. In thesecond-type precoding matrix, the structure of the precoding matrix witha rank of 4 may include at least one of the foregoing examples, or mayinclude a matrix that has a row and/or column transform relationshipwith U₂ ⁴ different from the foregoing examples.

Optionally, the precoding matrix with a rank of 4 meets at least one ofthe following:

${W_{11} = {\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}}},$

or

a matrix that has a row and/or column transform relationship with W₁₁.

It may be further learned from U₂ ⁴ that, the antenna port group #3 maybe used to send signals of two layers, that is, two streams, and theantenna port group #4 may be used to send signals of two layers, thatis, two streams. To ensure power equalization between different streams,a normalization coefficient may be obtained through normalizationprocessing. It is assumed that total transmit power is 1, and ¼ of thepower may be allocated to each of the four layers. That is, ¼ of thepower may be allocated to each row vector in the precoding matrix.Because coherent transmission may be performed on a signal stream ofeach layer through two antenna ports, ⅛ of the power may be furtherallocated to two antenna ports corresponding to each layer, and anormalization coefficient

$\frac{1}{\sqrt{8}}$

may be obtained. Therefore, W₁₁ and the matrix that has a row and/orcolumn transform relationship with W₁₁ may be considered as precodingmatrices that meet power equalization between streams, and

$\frac{1}{\sqrt{8}}$

may be considered as a normalization coefficient that meets powerequalization between streams.

Based on the foregoing design, the codebook may supportfour-antenna-port partial coherent transmission with any quantity oflayers within a range of [1, 4], which greatly improves transmissionflexibility. In addition, different requirements such as powerequalization between antenna ports or power equalization between streamsmay be met. In addition, based on partial coherent transmission, on asame time-frequency resource, one terminal device may send differentsignal streams based on different antenna port groups, or send signalsto different network devices based on different antenna port groups, andmay further perform coherent transmission based on antennas in a sameantenna port group, so as to improve signal quality.

It should be understood that the above-enumerated precoding matriceswith a rank of 4 are merely examples for description, and should notconstitute any limitation on this application. In the second-typeprecoding matrix, the precoding matrix with a rank of 4 may include amatrix obtained after the structure U₂ ⁴ of the precoding matrix with arank of 4 is transformed (such as normalization processing and/or rowand/or column transform), or a matrix that is different from theforegoing examples and obtained after a matrix that has a row and/orcolumn transform relationship with any one of the structure U₂ ⁴ of theprecoding matrix with a rank of 4 is transformed.

3. Third-type precoding matrix

Each element in the third-type precoding matrix is a non-zero element,and any two column vectors are orthogonal to each other.

That is, the third-type precoding matrix does not include a zeroelement.

It should be noted that, that two column vectors are orthogonal to eachother means that a product of a conjugate transpose of one column vectorin one precoding matrix and another column vector in a same precodingmatrix is zero. Any two column vectors are orthogonal to each other,that is, a result that a product is zero may be obtained by performingthe foregoing step for any two column vectors in a precoding matrix.

In a possible design, optionally, a structure of a precoding matrix witha rank of 4 meets at least one of the following:

${U_{3}^{4} = \begin{bmatrix}b_{k_{1}} & b_{k_{1}} & b_{k_{1} + {x_{1}O}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {{- \alpha}\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}} & {{- \alpha}\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

a matrix that has a row and/or column transform relationship with U₃ ⁴.

α∈{1,−1,j,−j}, j is an imaginary unit, b_(k) ₁ , b_(k) ₂ , b_(x) ₁ _(−x)₁ _(O), and b_(k) ₂ _(+x) ₂ _(O) are discrete Fourier transform DFTvectors and meet

${b_{i} = \begin{bmatrix}1 \\e^{j\frac{2\;\pi\; i}{{N/2} \cdot O}}\end{bmatrix}},\mspace{14mu}{i = {{\left\{ {k_{1},k_{2},{k_{1} + {x_{1}O}},{k_{2} + {x_{2}O}}} \right\}\mspace{14mu} 0} \leq i \leq {{\frac{N}{2} \cdot O} - 1}}},$

i is an integer, N is an antenna port quantity, and N=4. For a codebookwith four antenna ports, a value of O may be 2, and when O=2, x₁∈{0, 1},and x₂∈{0, 1}.

i={k₁, k₂, k₁+x₁O, k₂+x₂O} indicates that i may be k₁, k₂, k₁+x₁O, ork₂+x₂O. For example,

${b_{k_{1}} = \begin{bmatrix}1 \\e^{j\frac{2\;\pi\; k_{1}}{{N/2} \cdot O}}\end{bmatrix}},{b_{k_{2}} = \begin{bmatrix}1 \\e^{j\frac{2\;\pi\; k_{2}}{{N/2} \cdot O}}\end{bmatrix}},{b_{k_{1} + {x_{1}O}} = \begin{bmatrix}1 \\e^{j\frac{2\;\pi\;{({k_{1} + {x_{1}O}})}}{{N/2} \cdot O}}\end{bmatrix}},{and}$ ${b_{k_{2} + {x_{2}O}} = {{\begin{bmatrix}1 \\e^{j\frac{2\;\pi\;{({k_{1} + {x_{2}O}})}}{{N/2} \cdot O}}\end{bmatrix}.\mspace{14mu} 0} \leq i \leq {{\frac{N}{2} \cdot O} - 1}}};$

in addition, i is an integer, indicating that any one of {k₁, k₂,k₁+x₁O, k₂+x₂O} may be an integer in

$\left\lbrack {0,\ {{\frac{N}{2} \cdot O} - 1}} \right\rbrack.$

For example,

${0 \leq k_{1} \leq {{\frac{N}{2} \cdot O} - 1}},{0 \leq k_{2} \leq {{\frac{N}{2} \cdot O} - 1}},{0 \leq {k_{1} + {x_{1}O}} \leq {{\frac{N}{2} \cdot O} - 1}},{{{and}\mspace{14mu} 0} \leq {k_{2} + {x_{1}O}} \leq {{\frac{N}{2} \cdot O} - 1.}}$

Optionally, O may be an oversampling factor, and x₁ may be understood asa spacing between the DFT vector b_(k) ₁ in the structure of theprecoding matrix and a physical beam represented by the DFT vector, thatis, an oversampling factor whose beam spacing difference is x₁ times.Similarly, x₂ may be understood as a spacing between the DFT vectorb_(k) ₁ in the structure of the precoding matrix and a physical beamrepresented by the DFT vector, that is, an oversampling factor whosebeam spacing difference is x₂ times.

Optionally, a structure of a precoding matrix with a rank of 3 meets atleast one of the following:

${U_{3}^{3} = \begin{bmatrix}b_{k_{1}} & b_{k_{1}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {{- \alpha}\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

a matrix that has a row and/or column transform relationship with U₃ ³or

a matrix including any three columns in U₃ ⁴, or

a matrix including any three columns in the matrix that has a row and/orcolumn transform relationship with U₃ ⁴.

Optionally, a structure of a precoding matrix with a rank of 2 meets atleast one of the following.

${U_{3}^{2} = \begin{bmatrix}b_{k_{1}} & b_{k_{1} + {x_{1}O}} \\{\alpha\; b_{k_{2}}} & {\alpha\; b_{k_{2} + {x_{2}O}}}\end{bmatrix}},$

a matrix that has a row and/or column transform relationship with U₃ ²,or

a matrix including any two columns in U₃ ⁴, or

a matrix including any two columns in the matrix that has a row and/orcolumn transform relationship with U₃ ⁴.

Optionally, a structure of a precoding matrix with a rank of 1 meets atleast one of the following:

${U_{3}^{1} = \begin{bmatrix}b_{k_{1}} \\{\alpha\; b_{k_{2}}}\end{bmatrix}},$

a matrix that has a row and/or column transform relationship with U₃ ²,or

a matrix including any column in U₃ ⁴, or

a matrix including any column in the matrix that has a row and/or columntransform relationship with U₃ ⁴.

It should be understood that the foregoing enumerates a plurality ofpossible forms of structures of precoding matrices in codebookscorresponding to different ranks. However, this should not constituteany limitation on this application. In the third-type precoding matrix,the structure of the precoding matrix may include at least one of theforegoing examples, or may include a matrix that has a row and/or columntransform relationship with any one of the foregoing examples and thatis different from the foregoing examples. In addition, any precodingmatrix obtained through normalization processing and/or row/columnrelationship transform based on the structure of any possible precodingmatrix provided above should fall within the protection scope of thisapplication. For brevity, examples are not enumerated herein one by one.

In addition, it should be noted that, in this embodiment of thisapplication, different from an existing (for example, an LTE protocol)codebook, in a precoding matrix used for coherent transmission providedin this application, two discrete Fourier transform (DFT) vectorsincluded in each column vector may be two different DFT vectors, and arenot distinguished only by using a phase factor α. For ease ofunderstanding, FIG. 3 is a schematic diagram of an antenna port.

Antenna port groups in FIG. 3 may include two groups of antenna ports,and each X in the figure represents an antenna port group including twoantenna ports in different polarization directions. An antenna port #0and an antenna port #1 are antenna ports in a same polarizationdirection, and may be corresponding to a same DFT vector, for example,denoted as b₁. An antenna port #2 and an antenna port #3 are antennaports in a same polarization direction, and may be corresponding to asame DFT vector, for example, denoted as b₂, where b₁ and b₂ areorthogonal to each other. Alternatively, an antenna port #0 and anantenna port #2 are one group of antenna ports in different polarizationdirections, and may be corresponding to a same DFT vector, for example,denoted as b₁. An antenna port #1 and an antenna port #3 are anothergroup of antenna ports in different polarization directions, and may becorresponding to a same DFT vector, for example, denoted as b₂, where b₁and b₂ are orthogonal to each other. In this embodiment of thisapplication, a rank of 1 is used as an example. A structure of aprecoding matrix may be

${U_{3}^{1} = \begin{bmatrix}b_{k_{1}} \\{\alpha\; b_{k_{2}}}\end{bmatrix}},$

which is different from a structure

$\begin{bmatrix}b_{k_{1}} \\{\alpha\; b_{k_{1}}}\end{bmatrix},$

of a precoding matrix in an existing codebook. Therefore, it is notnecessary to require that two DFT vectors that constitute a same columnvector point to a same beam direction. In this way, a selection range ofthe precoding matrix may be expanded, so that a minimal Grassmanniandistance of the codebook is increased, thereby facilitating systemperformance improvement.

To facilitate understanding of the structures of the precoding matricesprovided above, the following describes in detail the above-enumeratedstructures of the precoding matrices with reference to detailedembodiments.

It is assumed that an antenna port quantity N is 4 and an oversamplingfactor O is 2, and b_(i) may be obtained as follows:

${b_{i} = \begin{bmatrix}1 \\1\end{bmatrix}},{{i = 0};\;{b_{i} = \begin{bmatrix}1 \\j\end{bmatrix}}},{{i = 1};}$ ${b_{i} = \begin{bmatrix}1 \\{- 1}\end{bmatrix}},{{i = 2};\;{{{and}\mspace{14mu} b_{i}} = \begin{bmatrix}1 \\{- j}\end{bmatrix}}},{i = 3.}$

For example, if k₁=0 and k₂=2, the following may be obtained:

${b_{0} = \begin{bmatrix}1 \\1\end{bmatrix}},{{{and}\mspace{14mu} b_{2}} = {\begin{bmatrix}1 \\{- 1}\end{bmatrix}.}}$

If a value of α is 1, an obtained structure of the precoding matrix witha rank of 1 may be

$\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalizationcoefficient ½, an obtained precoding matrix with a rank of 1 may be

${\frac{1}{2}\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}}.$

Herein, the normalization coefficient ½ may be used to implement powerequalization between antenna ports.

Given x₁=1 and x₂=1, an obtained structure of a precoding matrix with arank of 4 may be

$\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} \\{- 1} & 1 & 1 & {- 1}\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient ¼, an obtained precoding matrix with a rank of4 may be

${\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} \\{- 1} & 1 & 1 & {- 1}\end{bmatrix}}.$

Herein, the normalization coefficient ¼ may be used to implement powerequalization between streams.

A structure of a precoding matrix with a rank of 2 may include any twocolumns in the structure of the precoding matrix with a rank of 4. Forexample, the structure may be

$\begin{bmatrix}1 & 1 \\1 & 1 \\1 & {- 1} \\{- 1} & 1\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient

$\frac{1}{\sqrt{8}},$

an obtained precoding matrix with a rank of 2 may be

${\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 1 \\1 & 1 \\1 & {- 1} \\{- 1} & 1\end{bmatrix}}.$

Herein, the normalization coefficient

$\frac{1}{\sqrt{8}}$

may be used to implement power equalization between streams.

A structure of a precoding matrix with a rank of 3 may include any threecolumns in the structure of the precoding matrix with a rank of 4. Forexample, the structure may be

$\begin{bmatrix}1 & 1 & 1 \\1 & 1 & {- 1} \\1 & {- 1} & 1 \\{- 1} & 1 & 1\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient

$\frac{1}{\sqrt{12}},$

an obtained precoding matrix with a rank of 3 may be

${\frac{1}{\sqrt{12}}\begin{bmatrix}1 & 1 & 1 \\1 & 1 & {- 1} \\1 & {- 1} & 1 \\{- 1} & 1 & 1\end{bmatrix}}.$

Herein, the normalization coefficient

$\frac{1}{\sqrt{12}}$

may be used to implement power equalization between streams.

For another example, if k₁=0 and k₂=0, the following may be obtained:

$b_{0} = {\begin{bmatrix}1 \\1\end{bmatrix}.}$

If a value of α is j, x₁=1, and x₂=1, an obtained structure of theprecoding matrix with a rank of 4 may be

$\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\j & {- j} & j & {- j} \\j & {- j} & {- j} & j\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient ¼, an obtained precoding matrix with a rank of4 may be

${\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\j & {- j} & j & {- j} \\j & {- j} & {- j} & j\end{bmatrix}}.$

Herein, the normalization coefficient ¼ may be used to implement powerequalization between antenna ports.

For another example, if k₁=1 and k₂=1, the following may be obtained:

$b_{1} = {\begin{bmatrix}1 \\j\end{bmatrix}.}$

If a value of α is j, x₁=1, and x₂=1, an obtained structure of theprecoding matrix with a rank of 4 may be

$\begin{bmatrix}1 & 1 & 1 & 1 \\j & j & {- j} & {- j} \\1 & {- 1} & 1 & {- 1} \\j & {- j} & {- j} & j\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient ¼, an obtained precoding matrix with a rank of4 may be

$\begin{bmatrix}1 & 1 & 1 & 1 \\j & j & {- j} & {- j} \\1 & {- 1} & 1 & {- 1} \\j & {- j} & {- j} & j\end{bmatrix}.$

Herein, the normalization coefficient ¼ may be used to implement powerequalization between antenna ports.

For another example, if k₁=1 and k₂=3, the following may be obtained:

${b_{1}\begin{bmatrix}1 \\j\end{bmatrix}},{{{and}\mspace{14mu} b_{3}} = {\begin{bmatrix}1 \\{- j}\end{bmatrix}.}}$

If a value of α is j, x₁=1, and x₂=1, an obtained structure of theprecoding matrix with a rank of 4 may be

$\begin{bmatrix}1 & 1 & 1 & 1 \\j & j & {- j} & {- j} \\j & {- j} & j & {- j} \\1 & {- 1} & {- 1} & 1\end{bmatrix}.$

After normalization processing, for example, multiplication by anormalization coefficient ¼, an obtained precoding matrix with a rank of4 may be

${\frac{1}{4}\begin{bmatrix}1 & 1 & 1 & 1 \\j & j & {- j} & {- j} \\j & {- j} & j & {- j} \\1 & {- 1} & {- 1} & 1\end{bmatrix}}.$

Herein, the normalization coefficient ¼ may be used to implement powerequalization between antenna ports.

It should be understood that the above-enumerated structures of theprecoding matrices and precoding matrices are merely examples fordescription, and should not constitute any limitation on thisapplication. In the third-type precoding matrix, the precoding matrixmay further include a matrix obtained by performing row and/or columntransform on any one of the above-enumerated precoding matrices.

In addition, the structures of the precoding matrices with ranks of 1,2, or 3 may separately include any one column, two columns, or threecolumns in the structure of the precoding matrix with a rank of 4, andthe precoding matrices with ranks of 1, 2, and 3 may be separatelyobtained by multiplying the structures of the precoding matrices withranks of 1, 2, and 3 by one normalization coefficient. For example, thenormalization coefficient may be

$\frac{1}{\sqrt{M \cdot N}}.$

It should be further understood that the above-enumerated structures ofthe precoding matrices with ranks of 1, 2, 3, and 4 and thecorresponding precoding matrices are examples for description, andshould not constitute any limitation on this application. In thethird-type precoding matrix, the structure of the precoding matrix mayinclude at least one of the foregoing examples, or may include a matrixthat has a row and/or column transform relationship with any one of theforegoing examples and that is different from the foregoing examples. Inaddition, any precoding matrix obtained through normalization processingand/or row/column relationship transform based on the structure of anypossible precoding matrix provided above should fall within theprotection scope of this application. For brevity, examples are notenumerated herein one by one.

In another possible design, the third-type precoding matrix includesW_(M) where W_(M) includes M column vectors in W₀, and W₀ and anyprecoding matrix u in a codebook with a rank of 1 meet the followingmathematical transform relationship:

W _(o) =I−2uu ^(H) /u ^(H) u.

W_(M) represents a precoding matrix with a rank of M, M≥1 and M is aninteger, I is an identity matrix, and u^(H) is a conjugate transposematrix of u. In this embodiment of this application, for the codebookwith a rank of 1, refer to a codebook with a rank of 1 provided in anexisting protocol (for example, an LTE protocol). By way of example andnot limitation, precoding matrices in the codebook with a rank of 1 mayinclude:

${\frac{1}{2}\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\1 \\j \\j\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\1 \\{- 1} \\1\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\1 \\{- j} \\{- j}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\j \\1 \\j\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\j \\j \\1\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\j \\{- 1} \\{- j}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\j \\{- j} \\{- 1}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\1 \\{- 1}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\j \\{- j}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- 1} \\{- 1}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- j} \\j\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- j} \\1 \\{- j}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- j} \\j \\{- 1}\end{bmatrix}},{\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- 1} \\j\end{bmatrix}},{{and}\mspace{14mu}{{\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- j} \\1\end{bmatrix}}.}}$

If any one of the above-enumerated precoding matrices in the codebookwith a rank of 1 is denoted as w₁, optionally, a precoding matrix u inthe codebook with a rank of 1 further includes w₂, w₂ is taken from w₁′,and a Grassmannian distance between w₁ and w₂ is greater than or equalto

$\frac{1}{\sqrt{2}},$

and w₁′ and w₁ meet the following relationship:

$w_{1}^{\prime} = {\begin{bmatrix}a_{1} & 0 & 0 & 0 \\0 & a_{2} & 0 & 0 \\0 & 0 & a_{3} & 0 \\0 & 0 & 0 & a_{4}\end{bmatrix}w_{1}}$

α₁∈{1,−1,j,−j}, α₂∈{1,−1,j,−j}, α₃∈{1,−1,j,−j}, and α₄∈(1,−1,j,−j). Inthis embodiment of this application, values of α₁, α₂, α₃, and α₄ may bedefined in a protocol and may be the same or different. This is notlimited in this application.

Herein, the Grassmannian distance between w₁ and w₂ may be defined as

${{d\left( {w_{1},w_{2}} \right)} = {\frac{1}{\sqrt{2}}{{{w_{w}w_{1}^{H}} - {w_{2}w_{2}^{H}}}}_{F}}},$

where ∥·∥ represents a Frobenius norm of the matrix.

In this embodiment, the Grassmannian distance between w₁ and w₂ may beenabled to be greater than or equal to

$\frac{1}{\sqrt{2}}$

through selection of a₁, a₂, a₃, and a₄. For example, a₁=1, a₂=−1, a₃=0,and a₄=1.

It should be understood that specific calculation processes of theHouseholder mathematical transformation and the Grassmannian distancementioned herein may be the same as those in the prior art. For brevity,detailed description of the specific calculation processes thereof isomitted herein.

It should be further understood that the above-enumerated codebook witha rank of 1 is merely an example for description, and should notconstitute any limitation on this application. The codebook with a rankof 1 may include only the precoding matrix w₁ in the codebook with arank of 1 in the above-enumerated existing protocol (for example, an LTEprotocol), or may include only the precoding matrix w₂ with a rank of 1proposed in this application, or may include some or all of theabove-enumerated w₁ and w₂, or may even include a precoding matrix in acodebook with a rank of 1 defined in a future protocol. This is notlimited in this application.

It should be further understood that, the third-type precoding matrixW_(M) in this embodiment may include W_(M) precoding matrices in thecodebook with a rank of 1, or may include a matrix that has a row and/orcolumn transform relationship with a matrix formed by the M precodingmatrices. For brevity, examples are not enumerated herein one by one.

It should be noted that Wtf may include M column vectors in W₀, but thisdoes not mean that W_(M) may include any M column vectors in W₀. In aplurality of matrices that include any M column vectors in W₀, providedthat W_(M) includes at least one of the plurality of matrices, W_(M)should fall within the protection scope claimed by this application.

In still another possible design, the third-type precoding matrixincludes W_(M), where W_(M) includes M precoding matrices in a codebookwith a rank of 1, M is the rank, M≥1, and M is an integer.

The codebook with a rank of 1 may include the precoding matrix w₁ in thecodebook with a rank of 1 in the above-enumerated existing protocol (forexample, an LTE protocol), or may include the precoding matrix w₂ with arank of 1 proposed in this application, or may include some or all ofthe above-enumerated w₁ and w₂, or may even include a precoding matrixin a codebook with a rank of 1 defined in a future protocol. This is notlimited in this application.

It should be understood that, the third-type precoding matrix W_(M) inthis embodiment may include M precoding matrices in the codebook with arank of 1, or may include a matrix that has a row and/or columntransform relationship with a matrix formed by the any M precodingmatrices. For brevity, examples are not enumerated herein one by one.

It should be noted that W_(M) may include M column vectors in thecodebook with a rank of 1, but this does not mean that W_(M) may includeany M column vectors in the codebook with a rank of 1. In a plurality ofmatrices that include any M column vectors in the codebook with a rankof 1, provided that W_(M) includes at least one of the plurality ofmatrices, W_(M) should fall within the protection scope claimed by thisapplication.

Based on the foregoing three types of precoding matrices, the codebookmay support coherent transmission, partial coherent transmission, andnon-coherent transmission of four antenna ports with any quantity oflayers within a range of [1, 4], which greatly improves transmissionflexibility. In addition, different requirements such as powerequalization between antenna ports or power equalization between streamsmay be met. The terminal device may communicate with the network deviceon a same time-frequency resource by using a plurality of configuredantennas and based on different transmission forms, which improvesresource utilization and improves performance of the terminal device. Inaddition, in the designs of the various precoding matrices enumeratedabove, a selection range of the precoding matrix may be expanded,thereby increasing a minimal Grassmannian distance of the codebook, andfacilitating system performance improvement.

However, it should be understood that, possible forms offour-antenna-port precoding matrices with ranks of 1 to 4 are enumeratedin detail in this application, but this should not constitute anylimitation on this application. Matrices obtained after mathematicaltransformation or variation is performed based on the above-enumeratedprecoding matrices should fall within the protection scope of thisapplication. In addition, a four-antenna-port precoding matrix with arank greater than 4 may also be obtained based on a same concept. Forbrevity, details are not described herein with reference to detailedprecoding matrices.

Based on the foregoing design, the codebook may include at least twotypes of precoding matrices, but this does not mean that the codebook isdivided into three mutually independent parts. The at least two types ofprecoding matrices may be stored in a same codebook withoutdifferentiation, or may be defined as different codebook subsets basedon different types. This is not limited in this application.

In step 230, the terminal device precodes a signal based on theprecoding matrix (namely, the foregoing target precoding matrix)determined by using the PMI and the RI, to obtain a precoded signal.

Optionally, step 230 specifically includes:

determining, by the terminal device, the target precoding matrix basedon the PMI and the RI: and

precoding, by the terminal device, the signal based on the targetprecoding matrix to obtain the precoded signal.

Specifically, for a specific method for determining the target precodingmatrix by the terminal device based on the PMI and the RI, refer tomanner 1 to manner 6 described above. For brevity, details are notdescribed herein again. The terminal device may precode a to-be-sentsignal (for example, uplink data or uplink control signaling) based onthe target precoding matrix determined by using the PMI and the RI, soas to obtain a precoded signal.

It should be understood that a specific process in which the terminaldevice precodes the signal may be the same as that in the prior art. Forbrevity, a detailed description of the specific process is omittedherein.

In step 240, the terminal device sends the precoded signal.

Correspondingly, in step 240, the network device receives the precodedsignal.

It should be noted that, for ease of understanding only, a procedure inwhich the terminal device sends the precoded signal to the networkdevice is shown in the figure. However, actually, the terminal devicemay send the precoded signal to one or more network devices through aplurality of configured antenna ports. Therefore, in step 240, thenetwork device that receives the precoded signal may include only thenetwork device in step 210, or may include another network device inaddition to the network device in step 210, or may be a differentnetwork device than the network device in step 210. For example, theterminal device receives a PMI and an RI from a network device #1, andsends the precoded signal to a network device #2. The network device #1is an example of the network device in step 210. No limitation isimposed in this application on an object to which the terminal devicesends the signal.

Optionally, in step 240, the precoded signal sent by the terminal deviceto the network device may include precoded uplink data and a precodedDMRS, so that the network device determines an equivalent channel matrixbased on the DMRS, and further obtains, through demodulation, the uplinkdata sent by the terminal device.

It should be understood that a processing process after the networkdevice receives the precoded signal in step 240 may be the same as thatin the prior art. For brevity, detailed description of a specificprocess thereof is omitted herein.

Therefore, based on the foregoing designs, when the terminal device hasa corresponding capability, the terminal device may communicate with oneor more network devices in at least two transmission forms of coherenttransmission, partial coherent transmission, and non-coherenttransmission. Therefore, transmission flexibility of the terminal deviceis improved, and different transmission forms are used, so thatdifferent transmission requirements can be met, thereby facilitatingresource utilization improvement.

In this embodiment of this application, the network device may indicatethe target precoding matrix to the terminal device in a plurality ofpossible manners. With reference to different manners (including manner1 to manner 6), the following describes in detail a specific process inwhich the network device indicates the target precoding matrix and theterminal device determines the target precoding matrix based on thereceived PMI and RI.

It should be noted that, in the following plurality of possibleindication manners, the PMI may be used to indicate a codebook index,and each codebook index may be corresponding to one precoding matrix (ormay be referred to as a code word), or a one-to-one correspondencebetween a codebook index and a precoding matrix may be stored in thecodebook. That is, in a codebook corresponding to a same rank, thecodebook index and the precoding matrix may be in a one-to-onecorrespondence. Therefore, the PMI may be used to indicate a targetprecoding matrix in a codebook corresponding to a rank. For brevity, asame or similar case is not described below.

Manner 1

The network device may send fourth indication information and an RI,where the RI is used to indicate a rank of a precoding matrix, and thefourth indication information is used to indicate a target precodingmatrix in a codebook corresponding to the rank indicated by the RI.

In other words, in the codebook corresponding to a same rank, the fourthindication information is used to indicate one precoding matrix.Optionally, the fourth indication information may be a PMI.

For example, it is assumed that a plurality of precoding matrices arestored in the codebook, the rank may be indicated by the RI, and acodebook index corresponding to the target precoding matrix may beindicated by using the fourth indication information in the codebookcorresponding to the rank.

Correspondingly, in manner 1, the terminal device receives the fourthindication information and the RI, and determines the target precodingmatrix based on the fourth indication information and the RI.

Optionally, the fourth indication information and the RI are carried inDCI.

Manner 2

The network device may send fifth indication information and an RI,where the RI is used to indicate a rank of a precoding matrix, the fifthindication information may include two indication fields, a firstindication field in the two indication fields indicates at least onetype of a first-type precoding matrix, a second-type precoding matrix,or a third-type precoding matrix, and a second indication field in thetwo indication fields indicates a target precoding matrix in at leastone type of precoding matrix indicated by the first indication field ina codebook corresponding to the rank indicated by the RI.

In other words, the network device may carry two levels of indicationinformation by using one piece of indication information, so as toindicate the target precoding matrix to the terminal device. Optionally,the fifth indication information may be a PMI.

For example, it is assumed that a plurality of precoding matrices arestored in the codebook, and the rank may be indicated by the RI. In thecodebook corresponding to the rank, at least two types of precodingmatrices may be included, for example, at least two types of theforegoing three types of precoding matrices. The first indication fieldin the fifth indication information may indicate a type of an availableprecoding matrix. For example, the first indication field may be twobits, and a correspondence between the first indication field and a typeof a precoding matrix may be shown in Table 1 below.

TABLE 1 First indication field Type of a precoding matrix 00 First-typeprecoding matrix 01 Second-type precoding matrix 10 Third-type precodingmatrix

It can be seen that different values in the first indication field arecorresponding to different types of precoding matrices, and the secondindication field may indicate a target precoding matrix in a type of anavailable precoding matrix (namely, a type of a precoding matrixcorresponding to the first indication field). In this implementation,each type of precoding matrix may be indicated by using one set ofcodebook indexes. Specifically, when values in the first indicationfield are the same, that is, corresponding to one type of precodingmatrix, a value in the second indication field may be used to uniquelyindicate one precoding matrix. Therefore, in a codebook corresponding toa same rank, the first indication field and the second indication fieldin the fifth indication information are used to jointly indicate thetarget precoding matrix.

It should be understood that, in a same set of codebook indexes, eachindex value indicates one precoding matrix, that is, any two indexvalues in one set of codebook indexes are different. In two differentsets of codebook indexes, precoding matrices indicated by same indexvalues may be different. For brevity, a same or similar case is notdescribed below.

It should be further understood that the correspondence, between thefirst indication field and a type of a precoding matrix, enumerated inTable 1 is merely an example, and should not constitute any limitationon this application. For example, the correspondence between the firstindication field and a type of a precoding matrix may also be shown inTable 2 below.

TABLE 2 First indication field Type of a precoding matrix 00 First-typeprecoding matrix 01 First-type precoding matrix and second-typeprecoding matrix 10 First-type precoding matrix, second-type precodingmatrix, and third-type precoding matrix

In this implementation, when the first indication field has differentvalues, the second indication field is corresponding to one set ofcodebook indexes. When a type of a precoding matrix indicated by thefirst indication field is determined, precoding matrices in one or moretypes of precoding matrices indicated by the first indication field maybe in a one-to-one correspondence with codebook indexes. The networkdevice and the terminal device may pre-agree on a plurality of possibleone-to-one correspondences between a codebook index and a precodingmatrix. For example, when only the first-type precoding matrix is used,a precoding matrix in the first-type precoding matrix may becorresponding to one set of codebook indexes, and each codebook index iscorresponding to one precoding matrix. When only the first-typeprecoding matrix and the second-type precoding matrix are used,precoding matrices in the first-type precoding matrix and thesecond-type precoding matrix may be corresponding to one set of codebookindexes, and each codebook index is corresponding to one precodingmatrix. When the first-type precoding matrix, the second-type precodingmatrix, and the third-type precoding matrix are used, precoding matricesin the first-type precoding matrix, the second-type precoding matrix,and the third-type precoding matrix may be corresponding to one set ofcodebook indexes, and each codebook index is corresponding to oneprecoding matrix. It may be understood that, when only one or two typesof precoding matrices are used, a bit quantity of a codebook index maybe reduced, that is, bit overheads of the fifth indication informationmay be reduced. A one-to-one correspondence between a codebook index anda precoding matrix may be defined in a protocol or configured by usinghigher layer signaling. This is not limited in this application.

Alternatively, a same set of codebook indexes may be defined for thefirst-type precoding matrix, the second-type precoding matrix, and thethird-type precoding matrix. For example, codebook indexes of first-typeprecoding matrices are sequentially numbered from 0 to X₁, codebookindexes of second-type precoding matrices are sequentially numbered fromX₂+1 to X₃, and codebook indexes of third-type precoding matrices aresequentially numbered from X₄+1 to X₅, where X₂>X₁ and X₄>X₃. The firstindication field implicitly indicates that the first value of thecodebook index is 0, X₃+1, or X₅+1. That is, the codebook index of thefirst-type precoding matrix and the codebook index of the second-typeprecoding matrix may be continuous (for example, X₂=X₁), or may benon-continuous (for example, X₂>X₁), and the codebook index of thesecond-type precoding matrix and the codebook index of the third-typeprecoding matrix may be continuous (for example, X₄=X₃), or may benon-continuous (for example, X₄>X₃). This is not limited in thisapplication.

It should be understood that, when different types of precoding matricesare used, a method for determining a one-to-one correspondence between acodebook index and a precoding matrix may be pre-agreed, or a one-to-onecorrespondence between a codebook index and a precoding matrix may bedynanucally changed. A method for defining a correspondence between acodebook index and a precoding matrix is not limited in thisapplication.

Correspondingly, in manner 2, the terminal device receives the fifthindication information and the RI, and determines the target precodingmatrix based on the fifth indication information and the RI.

Optionally, the fifth indication information and the RI are carried inDCI.

Manner 3

The network device sends indication information #1 (namely, an exampleof first indication information), sixth indication information, and anRI, where the indication information #1 is used to indicate an availablecodebook subset, the RI is used to indicate a rank of a target precodingmatrix, and the sixth indication information is used to indicate atarget precoding matrix in the available codebook subset indicated bythe indication information #1 and in a codebook corresponding to therank indicated by the RI.

Implementation A:

Optionally, the indication information #1 is a codebook subsetrestriction (CSR).

Optionally, the CSR is carried in higher layer signaling. The higherlayer signaling may include, for example, an RRC message or a MAC-CEmessage.

Optionally, the sixth indication information is a PMI.

Optionally, the PMI and the RI are carried in DCI.

In this manner, in a codebook corresponding to a same RI, a value ineach PMI may uniquely indicate one precoding matrix.

It should be noted that the network device may further indicate a CSR ofa rank to the terminal device by using the higher layer signaling, sothat the terminal device determines an available codebook subset basedon the indication information #1 in a codebook corresponding to therestricted rank. Herein, the codebook subset may include at least onetype of a first-type precoding matrix, a second-type precoding matrix,and a third-type precoding matrix.

In a possible design, the indication information #1 may be a bitmap. Thebitmap may include a plurality of indication bits, each indication bitis corresponding to one codebook subset, and each indication bit is usedto indicate whether a precoding matrix in the corresponding codebooksubset is an available precoding matrix.

For example, if the codebook includes a first codebook subset (includinga first-type precoding matrix, for example), a second codebook subset(including a second-type precoding matrix, for example), and a thirdcodebook subset (including a third-type precoding matrix, for example),the three codebook subsets may be respectively corresponding to oneindication bit in the bitmap. In this case, the bitmap may include threeindication bits, and the three indication bits may be respectivelycorresponding to the three codebook subsets according to a sequence. Forexample, the first indication bit is corresponding to the first codebooksubset, the second indication bit is corresponding to the secondcodebook subset, and the third indication bit is corresponding to thethird codebook subset. When the indication bit is set to “0”, itindicates that a precoding matrix in the indicated codebook subset is anunavailable precoding matrix. When the indication bit is set to “1”, itindicates that a precoding matrix in the indicated codebook subset is anavailable precoding matrix.

It should be understood that when the bitmap is used to indicate whethera precoding matrix in a codebook subset is an available precodingmatrix, the bitmap may indicate that precoding matrices in one or morecodebook subsets are available precoding matrices at the same time. Thisis not limited in this application. When precoding matrices in one ormore codebook subsets are available precoding matrices, for acorrespondence between a codebook index and a precoding matrix, refer torelated description in manner 2 above. For brevity, details are notdescribed herein again. The network device may indicate the targetprecoding matrix to the terminal device by using the PMI based on thecorrespondence between a codebook index and a precoding matrix.

It should be further understood that the one-to-one correspondence,between the indication bit and a type of a precoding matrix, enumeratedabove is merely an example for description, and should not constituteany limitation on this application. A correspondence between eachindication bit and a type of a precoding matrix may be pre-agreed. Basedon the pre-agreed correspondence, the network device may indicate a typeof an available precoding matrix to the terminal device. It should befurther understood that information indicated by different values of theindication bits enumerated above is merely an example for description,and should not constitute any limitation on this application.

In another possible design, the indication information #1 may includeone indication field, and different values of the indication fieldindicate that different types of precoding matrices are to be used. Forexample, the indication field includes two bits, and a correspondencebetween the indication field and a type of a precoding matrix may beshown in Table 3 below.

TABLE 3 Indication information #1 Type of a precoding matrix 00First-type precoding matrix 01 Second-type precoding matrix 10Third-type precoding matrix

In this implementation, the network device may indicate, to the terminaldevice by using higher layer signaling, a set of available precodingmatrices. The set of available precoding matrices may be unchangedwithin a period of time, or may be semi-static. Therefore, compared withthe foregoing manners, w % ben the network device sends the PMI and theRI to the terminal device by using DCI, overheads of the PMI may bereduced. This is because the network device may indicate each type ofprecoding matrix by using one set of codebook indexes, each set ofcodebook indexes may be indicated by using one set of PMIs, a pluralityof sets of codebook indexes corresponding to different types ofprecoding matrices may be independent of each other, and a plurality ofsets of PMIs used to indicate codebook indexes of different types ofprecoding matrices may also be independent of each other. For example, acodebook index corresponding to a 0^(th) precoding matrix in precodingmatrices with a rank of 1 in first-type precoding matrices may be “00”,and the network device may indicate the precoding matrix by using, forexample, a PMI with a value of “00”. A value of a PMI corresponding to a0^(th) precoding matrix in precoding matrices with a rank of 1 insecond-type precoding matrices may also be “00”, and the network devicemay indicate the precoding matrix by using, for example, a PMI with avalue of “00”. A value of a PMI corresponding to a 0^(th) precodingmatrix in precoding matrices with a rank of 1 in third-type precodingmatrices may further be “00”, and the network device may furtherindicate the precoding matrix by using, for example, a PMI with a valueof “00”. However, if the type of the precoding matrix is not indicatedby using the higher layer signaling, precoding matrices with a rank of 1in the three types of precoding matrices may need to be indicated byusing a same set of PMIs. Therefore, PMIs corresponding to the 0^(th)precoding matrix in the precoding matrices with a rank of 1 in thefirst-type precoding matrices, the 0^(th) precoding matrix in theprecoding matrices with a rank of 1 in the second-type precodingmatrices, and the 0^(th) precoding matrix in the precoding matrices witha rank of 1 in the third-type precoding matrices need to bedistinguished by using different values. When a quantity of precodingmatrices included in a codebook is relatively large, relatively largebit overheads may be required. However, if the codebook is divided intothree codebook subsets, a quantity of precoding matrices in eachcodebook subset is definitely less than a total quantity of precodingmatrices in the codebook, and required bit overheads may besignificantly reduced.

It should be understood that the correspondence, between a value in theindication information #1 and a type of a precoding matrix, enumeratedin Table 3 is merely an example, and should not constitute anylimitation on this application. For example, the correspondence betweena value in the indication information #1 and a type of a precodingmatrix may also be shown in Table 4 below.

TABLE 4 Indication information #1 Type of a precoding matrix 00First-type precoding matrix 01 First-type precoding matrix andsecond-type precoding matrix 10 First-type precoding matrix, second-typeprecoding matrix, and third-type precoding matrix

In this implementation, when each value of the indication information #1is used, an indicated set of available precoding matrices may beindicated by using one set of codebook indexes, each set of codebookindexes may be indicated by using one set of PMIs, a plurality of setsof codebook indexes corresponding to a plurality of values of theindication information #1 may be independent of each other, and aplurality of sets of PMIs used to indicate codebook indexes of differenttypes of precoding matrices may also be independent of each other. Whena type of a precoding matrix indicated by the indication information #1is determined, precoding matrices in one or more types of precodingmatrices indicated by the indication information #1 may be in aone-to-one correspondence with codebook indexes. This implementation issimilar to manner 2. The network device and the terminal device maypre-agree on a plurality of possible one-to-one correspondences betweena codebook index and a precoding matrix. For example, when the value ofthe indication information #1 is “00”, only the first-type precodingmatrix is used, one set of codebook indexes may be used to indicate aprecoding matrix in the first-type precoding matrix, and each codebookindex is corresponding to one precoding matrix. When the value of theindication information #1 is “01”, only the first-type precoding matrixand the second-type precoding matrix are used, one set of codebookindexes may be used to indicate precoding matrices in the first-typeprecoding matrix and the second-type precoding matrix, and each codebookindex is corresponding to one precoding matrix. When the value of theindication information #1 is “10”, the first-type precoding matrix, thesecond-type precoding matrix, and the third-type precoding matrix areused, one set of codebook indexes may be used to indicate precodingmatrices in the first-type precoding matrix, the second-type precodingmatrix, and the third-type precoding matrix, and each codebook index iscorresponding to one precoding matrix. It may be understood that, whenonly one or two types of precoding matrices are used, a bit quantity ofa codebook index may be reduced, that is, bit overheads of the PMI maybe reduced.

It should be understood that the above-enumerated correspondence betweendifferent values of the indication information #1 and a type of theprecoding matrix is merely an example for description for ease ofunderstanding, and should not constitute any limitation on thisapplication.

Implementation B:

Optionally, the indication information #1 is a PMI (for example, denotedas a PMI #1).

Optionally, the sixth indication information is a PMI (for example,denoted as a PMI #2).

The indication information #1 and the sixth indication information maybe different PMIs.

Optionally, the indication information #1, the sixth indicationinformation, and the RI are carried in DCI.

It should be understood that, the indication information #1, the sixthindication information, and the RI may be carried in same DCI ordifferent DCI. This is not limited in this application.

A correspondence between the indication information #1 and a type of aprecoding matrix may be shown in Table 3 or Table 4 above, and aspecific method in which the sixth indication information is used toindicate the target precoding matrix is also described in detail above.For brevity, details are not described herein again.

Correspondingly, in manner 3, the terminal device receives theindication information #1, the sixth indication information, and the RI,and determines the target precoding matrix based on the indicationinformation #1, the sixth indication information, and the RI.

Manner 4

The network device sends indication information #2 (namely, anotherexample of the first indication information), sixth indicationinformation, and an RI, where the indication information #2 is used toindicate a set of available precoding matrices, the RI is used toindicate a rank of a precoding matrix in a codebook, and the sixthindication information is used to indicate a target precoding matrix inthe set of available precoding matrices indicated by the indicationinformation #2 and in a codebook corresponding to the rank indicated bythe RI.

Optionally, the indication information #2 is a CSR.

Optionally, the CSR is carried in higher layer signaling. The higherlayer signaling may include, for example, an RRC message or a MAC-CEmessage.

Optionally, the sixth indication information is a PMI.

Optionally, the PMI and the RI are carried in DCI.

In this manner, in a codebook corresponding to a same RI, a value ineach PMI may uniquely indicate one precoding matrix.

It should be noted that the network device may further indicate a CSR ofa rank to the terminal device by using the higher layer signaling, sothat the terminal device determines an available codebook subset basedon the indication information #2 in a codebook corresponding to therestricted rank. Herein, the codebook subset may include at least onetype of a first-type precoding matrix, a second-type precoding matrix,and a third-type precoding matrix.

In a possible design, the indication information #2 may be a bitmap. Thebitmap may include a plurality of indication bits, each indication bitis corresponding to one precoding matrix, and each indication bit isused to indicate whether the corresponding precoding matrix is anavailable precoding matrix.

For example, if the codebook includes a plurality of precoding matrices,the bitmap may include a plurality of indication bits, each indicationbit may be corresponding to one precoding matrix in the codebook, thenetwork device may set an indication bit corresponding to an availableprecoding matrix to “1”, and may set an indication bit corresponding toan unavailable precoding matrix to “0”.

In the codebook corresponding to the rank indicated by the RI, theavailable precoding matrix indicated by the indication information #2may be indicated by using one independent set of codebook indexes. Thatis, a precoding matrix in the available precoding matrix in the codebookcorresponding to the RI may be in a one-to-one correspondence with thecodebook index. For example, the network device and the terminal devicemay pre-agree on a method for determining the one-to-one correspondencebetween a codebook index and a precoding matrix. The network device mayindicate, by using the PMI, a codebook index corresponding to the targetprecoding matrix. For example, a value in the PMI is a codebook index.

The terminal device may determine, based on the PMI and the method thatis for determining the one-to-one correspondence between a codebookindex and a precoding matrix and that is pre-agreed with the networkdevice, the target precoding matrix indicated by the codebook index.

Therefore, when only one or two types of precoding matrices areapplicable, a bit quantity of the codebook index may be reduced, thatis, bit overheads of the PMI may be reduced.

Correspondingly, in manner 4, the terminal device receives theindication information #2, the sixth indication information, and the RI,and determines the target precoding matrix based on the first indicationinformation, the sixth indication information, and the RI.

Manner 5

The network device may send second indication information, where thesecond indication information is used to indicate a set of codebookscorresponding to a discrete Fourier transform spread OFDM(DFT-spread-OFDM) waveform.

The network device sends a PMI and an RI, where the RI is used toindicate a rank of a precoding matrix, and the PMI is used to indicate atarget precoding matrix in a codebook that is corresponding to the rankindicated by the RI and that is in the codebook corresponding to theDFT-s-OFDM waveform.

Specifically, the DFT-s-OFDM waveform may be understood as a waveform ina transmission mode. The set of codebooks corresponding to the waveformmay include at least one codebook corresponding to at least one rank,and each codebook includes a first-type precoding matrix and asecond-type precoding matrix. Transmission based on a DFT-s-OFDMwaveform may be understood as a transmission mode (for example, denotedas a transmission mode #1). The second indication information may beinformation indicating the set of codebooks corresponding to theDFT-s-OFDM waveform, or may be information indicating a DFT-s-OFDMwaveform, or may be information indicating a transmission mode. This isnot limited in this application.

Correspondingly, the terminal device receives the second indicationinformation, the second indication information indicating the codebookcorresponding to the DFT-s-OFDM waveform.

The terminal device receives the PMI and the RI, and determines thetarget precoding matrix based on the PMI and the RI.

After the network device indicates a type of the precoding matrix byusing the second indication information, the network device may indicatethe target precoding matrix by using the PMI and the RI. In the set ofcodebooks corresponding to the DFT-s-OFDM waveform, a precoding matrixand a codebook index may be in a one-to-one correspondence. Thisimplementation is similar to the implementation described with referenceto Table 2 in manner 2. For details, refer to related description inmanner 2. For brevity, details are not described herein again.

Optionally, the second indication information is carried in higher layersignaling, for example, an RRC message or a MAC-CE message.

Manner 6

The network device may send third indication information, where thethird indication information is used to indicate a set of codebookscorresponding to a cyclic prefix OFDM (CP-OFDM) waveform.

The network device sends a PMI and an RI, where the RI is used toindicate a rank of a precoding matrix, and the PMI is used to indicate atarget precoding matrix in a codebook that is corresponding to the rankindicated by the RI and that is in the codebook corresponding to theCP-OFDM waveform.

Specifically, the CP-OFDM waveform may be understood as a waveform in atransmission mode. The set of codebooks corresponding to the waveformincludes at least one codebook corresponding to at least one rank, andeach codebook includes a first-type precoding matrix, a second-typeprecoding matrix, and a third-type precoding matrix. Transmission basedon a CP-OFDM waveform may be understood as a transmission mode (forexample, denoted as a transmission mode #2). The third indicationinformation may be information indicating the set of codebookscorresponding to the CP-OFDM waveform, or may be information indicatinga CP-OFDM waveform, or may be information indicating a transmissionmode. This is not limited in this application.

Correspondingly, the terminal device receives the third indicationinformation, and indicates, based on the third indication information,the codebook corresponding to the CP-OFDM waveform.

The terminal device receives the PMI and the RI, and determines thetarget precoding matrix based on the PMI and the RI.

After the network device indicates a type of the precoding matrix byusing the third indication information, the network device may indicatethe target precoding matrix by using the PMI and the RI. In the codebookcorresponding to the CP-OFDM waveform, a precoding matrix and a codebookindex may be in a one-to-one correspondence. This implementation issimilar to the implementation described with reference to Table 2 inmanner 2. For details, refer to related description in manner 2. Forbrevity, details are not described herein again.

Optionally, the third indication information is carried in higher layersignaling, for example, an RRC message or a MAC-CE message.

It should be understood that the higher layer signaling used to carrythe second indication information in manner 5 and the higher layersignaling used to carry the third indication information in manner 6 maybe two pieces of different higher layer signaling, or may be indicatedby different indication fields of one piece of higher layer signaling,or may even be indicated by different values of a same indication fieldof one piece of higher layer signaling. When the higher layer signalingused to carry the second indication information in manner 5 and thehigher layer signaling used to carry the third indication information inmanner 6 may be two pieces of different higher layer signaling, thenetwork device may send only at least one of the higher layer signalingused to carry the second indication information and the higher layersignaling used to carry the third indication information.

Based on the foregoing possible implementations, it may be learned thatthe above-enumerated fourth indication information to sixth indicationinformation may be PMIs. However, in different implementations, contentindicated by the PMIs may be different, and information indicated by thePMIs in different implementations may be determined with reference torelated description above. For brevity, details are not described hereinagain. In other words, the network device may send one or more PMIs tothe terminal device. A quantity of PMIs is not limited in thisapplication.

Still further, in any one of the foregoing possible implementations, ifa type of an available precoding matrix includes first-type precodingmatrices, the network device may further indicate a type in availablefirst-type precoding matrices. For example, at least one of type A, typeB, or type C in the first-type precoding matrices is indicated by usinghigher layer signaling. By way of example and not limitation, the higherlayer signaling may include an RRC message or a MAC-CE message.

It should be understood that the above-enumerated specific forms of thehigher layer signaling are merely examples for description, and shouldnot constitute any limitation on this application. The higher layersignaling may be signaling from an RRC layer, a MAC layer, or anotherprotocol layer different from a physical layer.

It should be understood that the above-enumerated precoding matrices areonly possible forms of the precoding matrices provided in thisapplication, and should not constitute any limitation on thisapplication. Precoding matrices obtained by performing row and/or columntransform or other mathematical transformation on the forms of theprecoding matrices provided in this application should fall within theprotection scope of this application.

It should be noted that, in a possible implementation, the networkdevice and the terminal device may store one or more of the following:

(a) a parameter used to obtain any one of the precoding matricesenumerated in the foregoing implementations, where any one of theforegoing precoding matrices may be obtained based on the parameter, forexample, the parameter may include but is not limited to theabove-enumerated codebook configuration parameter:

(b) any one of the precoding matrices enumerated in the foregoingimplementations:

(c) a matrix extended based on any one of the precoding matricesenumerated in the foregoing implementations:

(d) a matrix obtained by performing row/column transform on any one ofthe precoding matrices enumerated in the foregoing implementations;

(e) a matrix extended based on a matrix obtained by performingrow/column transform on any one of the precoding matrices enumerated inthe foregoing implementations; and

(f) a codebook, where the codebook includes at least one of the matricesin (b), (c). (d), or (e).

It should be understood that row/column transform refers to rowtransform, or column transform, or row transform and column transform inthis application.

The storing in this application may be storing in one or more memories.The one or more memories may be separately disposed, or may beintegrated into an encoder, a decoder, a processor, or a communicationsapparatus. Alternatively, some of the one or more memories areseparately disposed, and some of the one or more memories are integratedinto a decoder, a processor, or a communications apparatus. A type ofthe memory may be any form of storage medium. This is not limited inthis application.

It should be further understood that the foregoing “pre-agreement” maybe implemented by pre-storing corresponding code or a correspondingtable on devices (for example, including the terminal device and thenetwork device) or in another manner that may be used to indicaterelated information, and a specific implementation thereof is notlimited in this application.

The foregoing describes in detail the communication method in theembodiment of this application with reference to FIG. 2 and FIG. 3. Thefollowing describes in detail a communications apparatus in theembodiment of this application with reference to FIG. 4 to FIG. 6.

FIG. 4 is a schematic structural diagram of a terminal device accordingto an embodiment of this application. The terminal device may be appliedto the system shown in FIG. 1, and perform a function of the terminaldevice in the foregoing method embodiment. For ease of description, FIG.4 shows only main components of the terminal device. As shown in FIG. 4,a terminal device 40 includes a processor, a memory, a control circuit,an antenna, and an input/output apparatus. The processor is mainlyconfigured to process a communications protocol and communication data,control the entire terminal device, execute a software program, andprocess data of the software program. For example, the processor isconfigured to support the terminal device in performing an actiondescribed in the foregoing method embodiment, for example, determining aprecoding matrix based on received PMI and RI, so as to precode a signaland send a precoded signal. The memory is mainly configured to store asoftware program and data, for example, store a correspondence, betweenindication information and combination information, described in theforegoing embodiment. The control circuit is mainly configured toperform conversion between a baseband signal and a radio frequencysignal, and process the radio frequency signal. A combination of thecontrol circuit and the antenna may also be referred to as a transceiverthat is mainly configured to send/receive a radio frequency signal in anelectromagnetic wave form. The input/output apparatus such as atouchscreen, a display screen, or a keyboard is mainly configured toreceive data entered by a user, and output data to the user.

After the terminal device is powered on, the processor may read thesoftware program in the storage unit, interpret and execute aninstruction of the software program, and process data of the softwareprogram. When the processor needs to send data by using the antenna,after performing baseband processing on the to-be-sent data, theprocessor outputs a baseband signal to a radio frequency circuit. Afterperforming radio frequency processing on the baseband signal, the radiofrequency circuit sends a radio frequency signal in an electromagneticwave form by using the antenna. When data is sent to the terminaldevice, the radio frequency circuit receives a radio frequency signal byusing the antenna, converts the radio frequency signal into a basebandsignal, and outputs the baseband signal to the processor. The processorconverts the baseband signal into data, and processes the data.

A person skilled in the art may understand that for ease of description,FIG. 4 shows only one memory and only one processor. An actual terminaldevice may have a plurality of processors and a plurality of memories.The memory may also be referred to as a storage medium, a storagedevice, or the like. This is not limited in this embodiment of thisapplication.

In an optional implementation, the processor may include a basebandprocessor and a central processing unit. The baseband processor ismainly configured to process a communications protocol and communicationdata, and the central processing unit is mainly configured to controlthe entire terminal device, execute a software program, and process dataof the software program. Functions of the baseband processor and thecentral processing unit may be integrated into the processor in FIG. 4.A person skilled in the art may understand that the baseband processorand the central processing unit may alternatively be processorsindependent of each other, and are interconnected by using a technologysuch as a bus. A person skilled in the art may understand that theterminal device may include a plurality of baseband processors to adaptto different network standards, the terminal device may include aplurality of central processing units to improve a processing capabilityof the terminal device, and components of the terminal device may beconnected by using various buses. The baseband processor may also beexpressed as a baseband processing circuit or a baseband processingchip. The central processing unit may also be expressed as a centralprocessing circuit or a central processing chip. A function ofprocessing a communications protocol and communication data may beembedded into the processor, or may be stored in the storage unit in aform of a software program. The processor executes the software programto implement a baseband processing function.

In this embodiment of this application, the antenna that has atransceiver function and the control circuit may be considered as atransceiver unit 401 of the terminal device 40. For example, thetransceiver unit 401 is configured to support the terminal device inperforming the receiving function and the sending function described inFIG. 2. The processor that has a processing function is considered as aprocessing unit 402 of the terminal device 40. As shown in FIG. 4, theterminal device 40 includes the transceiver unit 401 and the processingunit 402. The transceiver unit may also be referred to as a transceivermachine, a transceiver, a transceiver apparatus, or the like.Optionally, a component that is in the transceiver unit 401 and that isconfigured to implement a receiving function may be considered as areceiving unit, and a component that is in the transceiver unit 401 andthat is configured to implement a sending function may be considered asa sending unit. In other words, the transceiver unit 401 includes thereceiving unit and the sending unit. The receiving unit may also bereferred to as a receiver, an input port, a receiver circuit, or thelike, and the sending unit may be referred to as a transmitter machine,a transmitter, a transmitter circuit, or the like.

The processor 402 may be configured to execute an instruction stored inthe memory, to control the transceiver unit 401 to receive a signaland/or send a signal, so as to complete a function of the terminaldevice in the foregoing method embodiment. In an implementation, afunction of the transceiver unit 401 may be implemented by using atransceiver circuit or a dedicated transceiver chip.

FIG. 5 is a schematic structural diagram of a network device accordingto an embodiment of this application, for example, may be a schematicstructural diagram of a base station. As shown in FIG. 5, the basestation may be applied to the system shown in FIG. 1, and implement afunction of the network device in the foregoing method embodiment. Abase station 50 may include one or more radio frequency units such asremote radio units (RRU) 501 and one or more baseband units (BBU) (whichmay also be referred to as digital units (DU)) 502. The RRU 501 may bereferred to as a transceiver unit, a transceiver, a transceiver circuit,a transceiver machine, or the like, and may include at least one antenna5011 and a radio frequency unit 5012. The RRU 501 is mainly configuredto receive and send a radio frequency signal and perform conversionbetween a radio frequency signal and a baseband signal, for example,configured to send the signaling message in the foregoing embodiments toa terminal device. The BBU 502 is mainly configured to perform basebandprocessing, control the base station, and the like. The RRU 501 and theBBU 502 may be physically disposed together, or may be physicallydisposed separately, to be specific, may be comprised in a distributedbase station.

The BBU 502 is a control center of the base station, may also bereferred to as a processing unit, and is mainly configured to implementa baseband processing function, for example, channel coding,multiplexing, modulation, and spreading. For example, the BBU (theprocessing unit) 502 may be configured to control the base station toperform an operation procedure related to the network device in theforegoing method embodiment.

In an instance, the BBU 502 may include one or more boards, and aplurality of boards may jointly support a radio access network (forexample, an LTE network) of a single access technology, or mayseparately support radio access networks (such as an LTE network, a 5Gnetwork, or another network) of different access technologies. The BBU502 further includes a memory 5021 and a processor 5022, where thememory 5021 is configured to store necessary instructions and data. Forexample, the memory 5021 stores the correspondence between a codebookindex and a precoding matrix in the foregoing embodiment. The processor5022 is configured to control the base station to perform a necessaryaction. For example, the processor 5022 is configured to control thebase station to perform the operation procedure related to the networkdevice in the foregoing method embodiment. The memory 5021 and theprocessor 5022 may serve one or more boards. In other words, a memoryand a processor may be disposed separately on each board, or a pluralityof boards may share a same memory and a same processor. In addition, anecessary circuit may be further disposed on each board.

FIG. 6 is a schematic structural diagram of a communications apparatus600. The apparatus 600 may be configured to implement the methoddescribed in the foregoing method embodiment. For details, refer todescription in the foregoing method embodiment. The communicationsapparatus 600 may be a chip, a network device (for example, a basestation), a terminal device, another network device, or the like.

The communications apparatus 600 includes one or more processors 601.The processor 601 may be a general-purpose processor, a dedicatedprocessor, or the like. For example, the processor 601 may be a basebandprocessor or a central processing unit. The baseband processor may beconfigured to process a communications protocol and communication data.The central processing unit may be configured to control thecommunications apparatus (for example, a base station, a terminal, or achip), execute a software program, and process data of the softwareprogram. The communications apparatus may include a transceiver unit,configured to implement input (receiving) and output (sending) of asignal. For example, the communications apparatus may be a chip, and thetransceiver unit may be an input and/or output circuit or acommunications interface of the chip. The chip may be used by aterminal, a base station, or another network device. For anotherexample, the communications apparatus may be a terminal, a base station,or another network device, and the transceiver unit may be a transceiveror a radio frequency chip.

The communications apparatus 600 includes one or more processors 601,and the one or more processors 601 may implement the method performed bythe network device or the terminal device in the embodiment shown inFIG. 2.

In a possible design, the communications apparatus 600 includes a meansfor generating a PMI and an RI and a means for sending the PMI and theRI. Functions of the means for generating the PMI and the RI and themeans for sending the PMI and the RI may be implemented by using one ormore processors. For example, the PMI and the RI may be generated byusing one or more processors, and sent by using a transceiver, aninput/output circuit, or an interface of a chip. For the PMI and the RI,refer to related description in the foregoing method embodiment.

In a possible design, the communications apparatus 600 includes a meansfor receiving a PMI and an RI, and a means for determining a precodingmatrix and precoding a signal. For the PMI, the RI, and how to determinethe precoding matrix, refer to related description in the foregoingmethod embodiment. For example, the PMI and the RI may be received byusing a transceiver, or an input/output circuit, or an interface of achip, a precoded signal may be sent by using the transceiver, or theinput/output circuit, or the interface of a chip, the precoding matrixis determined based on the PMI and the RI by using one or moreprocessors, and a signal is precoded based on the PMI and the RI byusing one or more processors.

Optionally, the processor 601 may further implement another function inaddition to the method in the embodiment shown in FIG. 2.

Optionally, in a design, the processor 601 may further include aninstruction 603. The instruction may run on the processor, so that thecommunications apparatus 600 performs the method described in theforegoing method embodiment.

In another possible design, the communications apparatus 600 mayalternatively include a circuit. The circuit may implement the functionof the network device or the terminal device in the foregoing methodembodiment.

In still another possible design, the communications apparatus 600 mayinclude one or more memories 602. The one or more memories 600 store aninstruction 604. The instruction may run on the processor, so that thecommunications apparatus 600 performs the method described in theforegoing method embodiment. Optionally, the memory may further storedata. Optionally, the processor may also store an instruction and/ordata. For example, the one or more memories 602 may store thecorrespondence, between indication information and a type of a precodingmatrix, described in the foregoing embodiment, or a related parameter,table, or the like in the foregoing embodiment. The processor and thememory may be disposed separately, or may be integrated together.

In yet another possible design, the communications apparatus 600 mayfurther include a transceiver unit 605 and an antenna 606. The processor601 may be referred to as a processing unit, and controls thecommunications apparatus (a terminal or a base station). The transceiverunit 605 may be referred to as a transceiver, a transceiver circuit, atransceiver machine, or the like, and is configured to implement atransceiver function of the communications apparatus by using theantenna 606.

This application further provides a communications system, including theforegoing one or more network devices and one or more terminal devices.

It should be understood that, the processor in the embodiments of thisapplication may be a central processing unit (CPU), the processor mayfurther be another general-purpose processor, a digital signal processor(DSP), an application-specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or another programmable logicaldevice, discrete gate or transistor logical device, discrete hardwarecomponent, or the like. The general-purpose processor may be amicroprocessor, or the processor may be any conventional processor orthe like.

It should be further understood that the memory in the embodiments ofthis application may be a volatile memory or a nonvolatile memory, ormay include both a volatile memory and a nonvolatile memory. Thenonvolatile memory may be a read-only memory (ROM), a programmableread-only memory (PROM), an erasable programmable read-only memory(erasable PROM, EPROM), an electrically erasable programmable read-onlymemory (electrically EPROM, EEPROM), or a flash memory. The volatilememory may be a random access memory (RAM), used as an external cache.Through example but not limitative description, many forms of randomaccess memories (RAM) may be used, for example, a static random accessmemory (static RAM, SRAM), a dynamic random access memory (DRAM), asynchronous dynamic random access memory (synchronous DRAM, SDRAM), adouble data rate synchronous dynamic random access memory (double datarate SDRAM, DDR SDRAM), an enhanced synchronous dynamic random accessmemory (enhanced SDRAM, ESDRAM), a synchronous link dynamic randomaccess memory (synchlink DRAM, SLDRAM), and a direct rambus randomaccess memory (direct rambus RAM, DR RAM).

All or some of the foregoing embodiments may be implemented by usingsoftware, hardware, firmware, or any combination thereof. When softwareis used to implement the embodiments, the foregoing embodiments may beimplemented completely or partially in a form of a computer programproduct. The computer program product includes one or more computerinstructions or computer programs.

When the program instructions or the computer programs are loaded orexecuted on a computer, the procedures or functions according to theembodiments of this application are all or partially generated.

The computer may be a general-purpose computer, a dedicated computer, acomputer network, or another programmable apparatus. The computerinstructions may be stored in a computer-readable storage medium or maybe transmitted from a computer-readable storage medium to anothercomputer-readable storage medium. For example, the computer instructionsmay be transmitted from a website, computer, server, or data center toanother website, computer, server, or data center in a wired (forexample, infrared, radio, and microwave) manner. The computer-readablestorage medium may be any usable medium accessible by the computer, or adata storage device, such as a server or a data center, integrating oneor more usable media. The usable medium may be a magnetic medium (forexample, a floppy disk, a hard disk, or a magnetic tape), an opticalmedium (for example, a DVD), or a semiconductor medium. Thesemiconductor medium may be a solid-state drive.

It should be understood that the term “and/or” in this specificationdescribes only an association relationship for describing associatedobjects and represents that three relationships may exist. For example,A and/or B may represent the following three cases: Only A exists, bothA and B exist, and only B exists. In addition, the character “/” in thisspecification is usually a simplified form of “and/or”.

It should be understood that sequence numbers of the foregoing processesdo not mean execution sequences in various embodiments of thisapplication. The execution sequences of the processes should bedetermined according to functions and internal logic of the processes,and should not be construed as any limitation on the implementationprocesses of the embodiments of this application.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware or a combination of computer software and electronichardware. Whether the functions are performed by hardware or softwaredepends on particular applications and design constraint conditions ofthe technical solutions. A person skilled in the art may use differentmethods to implement the described functions for each particularapplication, but it should not be considered that the implementationgoes beyond the scope of this application.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiment, and detailsare not described herein again.

In the several embodiments provided in this application, it should beunderstood that the disclosed system, apparatus, and method may beimplemented in other manners. For example, the described apparatusembodiment is merely an example. For example, the unit division ismerely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,may be located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected based on actualrequirements to achieve the objectives of the solutions of theembodiments.

In addition, functional units in the embodiments of this application maybe integrated into one processing unit, or each of the units may existalone physically, or two or more units are integrated into one unit.

When the functions are implemented in the form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of this application essentially,or the part contributing to the prior art, or some of the technicalsolutions may be implemented in a form of a software product. Thecomputer software product is stored in a storage medium, and includesseveral instructions for instructing a computer device (which may be apersonal computer, a server, or a network device) to perform all or someof the steps of the methods described in the embodiments of thisapplication. The foregoing storage medium includes: any medium that canstore program code, such as a USB flash drive, a removable hard disk, aread-only memory (ROM), a random access memory (RAM), a magnetic disk,or an optical disc.

The foregoing descriptions are merely specific implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication shall fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

1. A communication method, comprising: sending first indicationinformation through a higher layer signaling to a terminal device, thefirst indication information indicating an available codebook subset;sending downlink control information, which indicates a transmissionprecoding matrix indicator (TPMI) and a transmission rank, to theterminal device; and receiving a signal from the terminal device,wherein the signal is based on a precoding matrix which belongs to theavailable codebook subset indicated by the first indication informationand corresponds to the TPMI and the transmission rank indicated by thedownlink control information; wherein the available codebook subset is afirst codebook subset, a second codebook subset, or a third codebooksubset, the first codebook subset comprising a first-type precodingmatrix, the second codebook subset comprising the first-type precodingmatrix and a second-type precoding matrix, the third codebook subsetcomprising the first-type precoding matrix, the second-type precodingmatrix, and a third-type precoding matrix; and wherein the first-typeprecoding matrix is non-coherent precoding, the second-type precodingmatrix is partial-coherent precoding, and the third-type precodingmatrix is coherent precoding.
 2. The method according to claim 1,wherein each column vector of any matrix in the first-type precodingmatrix comprises only one non-zero element, wherein non-zero elements inany two column vectors are located in different rows, wherein at leastone column vector of any matrix in the second-type precoding matrixcomprises at least one zero element and at least two non-zero elements,wherein each element in any matrix in the third-type precoding matrix isa non-zero element, and wherein any two column vectors of any matrix inthe third-type precoding matrix are orthogonal to each other when atransmission rank is greater than
 1. 3. The method according to claim 1,wherein the first indication information comprises one indication field,wherein a first value of the indication field indicates the firstcodebook subset, wherein a second value of the indication fieldindicates the second codebook subset, and wherein a third value of theindication field indicates the third codebook subset.
 4. The methodaccording to claim 1, wherein bit quantities of codebook indexes fordifferent available codebook subsets are different, and wherein thecodebook indexes are carried in the downlink control information.
 5. Themethod according to claim 4, wherein a bit quantity of codebook indexesfor the first codebook subset is less than that of codebook indexes forthe third codebook subset.
 6. The method according to claim 4, wherein abit quantity of codebook indexes for the second codebook subset is lessthan that of codebook indexes for the third codebook subset.
 7. Themethod according to claim 1, wherein the first-type precoding matrixcomprises at least one of: ${W_{1} = {\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₁.
 8. The method according to claim 1,wherein the first-type precoding matrix comprises at least one of:${W_{4} = {\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₄.
 9. The method according to claim 1,wherein the second-type precoding matrix comprises at least one of:${W_{11} = {\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₁₁, wherein φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j},and j is an imaginary unit.
 10. An apparatus, comprising: at least oneprocessor; and at least one memory coupled to the at least one processorand storing programming instructions for execution by the at least oneprocessor to cause the apparatus to perform operations comprising:sending first indication information through a higher layer signaling toa terminal device, the first indication information indicating anavailable codebook subset; sending downlink control information, whichindicates a transmission precoding matrix indicator (TPMI) and atransmission rank, to the terminal device; and receiving a signal fromthe terminal device, wherein the signal is based on a precoding matrixwhich belongs to the available codebook subset indicated by the firstindication information and corresponds to the TPMI and the transmissionrank indicated by the downlink control information; wherein theavailable codebook subset is a first codebook subset, a second codebooksubset, or a third codebook subset, the first codebook subset comprisinga first-type precoding matrix, the second codebook subset comprising thefirst-type precoding matrix and a second-type precoding matrix, thethird codebook subset comprising the first-type precoding matrix, thesecond-type precoding matrix, and a third-type precoding matrix; andwherein the first-type precoding matrix is non-coherent precoding, thesecond-type precoding matrix is partial-coherent precoding, and thethird-type precoding matrix is coherent precoding.
 11. The apparatusaccording to claim 10, wherein each column vector of any matrix in thefirst-type precoding matrix comprises only one non-zero element, whereinnon-zero elements in any two column vectors are located in differentrows, wherein at least one column vector of any matrix in thesecond-type precoding matrix comprises at least one zero element and atleast two non-zero elements, wherein each element in any matrix in thethird-type precoding matrix is a non-zero element, and wherein any twocolumn vectors of any matrix in the third-type precoding matrix areorthogonal to each other when a transmission rank is greater than
 1. 12.The apparatus according to claim 10, wherein the first indicationinformation comprises one indication field, wherein a first value of theindication field indicates the first codebook subset, wherein a secondvalue of the indication field indicates the second codebook subset, andwherein a third value of the indication field indicates the thirdcodebook subset.
 13. The apparatus according to claim 10, wherein bitquantities of codebook indexes for different available codebook subsetsare different, and wherein the codebook indexes are carried in thedownlink control information.
 14. The apparatus according to claim 13,wherein a bit quantity of codebook indexes for the first codebook subsetis less than that of codebook indexes for the third codebook subset. 15.The apparatus according to claim 13, wherein a bit quantity of codebookindexes for the second codebook subset is less than that of codebookindexes for the third codebook subset.
 16. The apparatus according toclaim 10, wherein the first-type precoding matrix comprises at least oneof: ${W_{1} = {\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 0 \\0 & 0\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₁.
 17. The apparatus according to claim 10,wherein the first-type precoding matrix comprises at least one of:${W_{4} = {\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\0 & 0 & 0\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₄.
 18. The apparatus according to claim 10,wherein the second-type precoding matrix comprises at least one of:${W_{11} = {\frac{1}{\sqrt{8}}\begin{bmatrix}1 & 0 & 1 & 0 \\0 & 1 & 0 & 1 \\\varphi_{1} & 0 & {- \varphi_{1}} & 0 \\0 & \varphi_{2} & 0 & {- \varphi_{2}}\end{bmatrix}}},$ or a matrix that has at least one of a row or a columntransform relationship with W₁₁, wherein φ₁∈{1,−1,j,−j}, φ₂∈{1,−1,j,−j},and j is an imaginary unit.
 19. A non-transitory computer-readablestorage medium comprising instructions which, when executed by at leastone processor, cause an apparatus including the at least one processorto perform operations comprising: sending first indication informationthrough a higher layer signaling to a terminal device, the firstindication information indicating an available codebook subset; sendingdownlink control information, which indicates a transmission precodingmatrix indicator (TPMI) and a transmission rank, to the terminal device;and receiving a signal from the terminal device, wherein the signal isbased on a precoding matrix which belongs to the available codebooksubset indicated by the first indication information and corresponds tothe TPMI and the transmission rank indicated by the downlink controlinformation; wherein the available codebook subset is a first codebooksubset, a second codebook subset, or a third codebook subset, the firstcodebook subset comprising a first-type precoding matrix, the secondcodebook subset comprising the first-type precoding matrix and asecond-type precoding matrix, the third codebook subset comprising thefirst-type precoding matrix, the second-type precoding matrix, and athird-type precoding matrix; and wherein the first-type precoding matrixis non-coherent precoding, the second-type precoding matrix ispartial-coherent precoding and the third-type precoding matrix iscoherent precoding.
 20. The storage medium according to claim 19,wherein each column vector of any matrix in the first-type precodingmatrix comprises only one non-zero element, wherein non-zero elements inany two column vectors are located in different rows, wherein at leastone column vector of any matrix in the second-type precoding matrixcomprises at least one zero element and at least two non-zero elements,wherein each element in any matrix in the third-type precoding matrix isa non-zero element, and wherein any two column vectors of any matrix inthe third-type precoding matrix are orthogonal to each other when atransmission rank is greater than
 1. 21. A system, comprising a firstapparatus and a second apparatus, wherein the first apparatus isconfigured to: send first indication information through a higher layersignaling to the second apparatus, the first indication informationindicating an available codebook subset; and send downlink controlinformation, which indicates a transmission precoding matrix indicator(TPMI) and a transmission rank, to the second apparatus; wherein thesecond apparatus is configured to: receive the first indicationinformation through the higher layer signaling; receive the downlinkcontrol information; determine a precoding matrix corresponding to theTPMI and the transmission rank obtained from the downlink controlinformation, wherein the precoding matrix belongs to the availablecodebook subset indicated by the first indication information; precode asignal based on the determined precoding matrix; and send the precodedsignal to the first apparatus; and wherein the first apparatus isfurther configured to receive the precoded signal; wherein the availablecodebook subset is a first codebook subset, a second codebook subset, ora third codebook subset, the first codebook subset comprising afirst-type precoding matrix, the second codebook subset comprising thefirst-type precoding matrix and a second-type precoding matrix, thethird codebook subset comprising the first-type precoding matrix, thesecond-type precoding matrix, and a third-type precoding matrix; andwherein the first-type precoding matrix is non-coherent precoding, thesecond-type precoding matrix is partial-coherent precoding and thethird-type precoding matrix is coherent precoding.
 22. The systemaccording to claim 21, wherein each column vector of any matrix in thefirst-type precoding matrix comprises only one non-zero element, whereinnon-zero elements in any two column vectors are located in differentrows, wherein at least one column vector of any matrix in thesecond-type precoding matrix comprises at least one zero element and atleast two non-zero elements, wherein each element in any matrix in thethird-type precoding matrix is a non-zero element, and wherein any twocolumn vectors of any matrix in the third-type precoding matrix areorthogonal to each other when a transmission rank is greater than
 1. 23.The system according to claim 21, wherein bit quantities of codebookindexes for different available codebook subsets are different, andwherein the codebook indexes are carried in the downlink controlinformation.